Comparison Expression

Simple Comparison Expression

A comparison expression is an expression that is included in the WHERE clause of the SELECT, UPDATE and DELETE statements, and in the HAVING clause of the SELECT statement. There are simple comparison, ANY / SOME / ALL, BETWEEN, EXISTS, IN / NOT IN, LIKE and IS NULL comparison expressions, depending on the kinds of the operators combined.

A simple comparison expression compares two comparable data values. Expressions or subqueries are specified as operands, and the comparison expression always returns NULL if one of the operands is NULL. The following table shows operators that can be used in the simple comparison expressions. For details, see Comparison Operators.

Comparison Operators

Comparison Operator Description Comparison Expression Return Value
= A value of left operand is the same as that of right operand. 1=2 0
<> , != A value of left operand is not the same as that of right operand. 1<>2 1
> A value of left operand is greater than that of right operand. 1>2 0
< A value of left operand is less than that of right operand. 1<2 1
>= A value of left operand is equal to or greater than that of right operand. 1>=2 0
<= A value of left operand is equal to or less than that of right operand. 1<=2 1

ANY/SOME/ALL quantifiers

A comparison expression that includes quantifiers such as ANY/SOME/ALL performs comparison operation on one data value and on some or all values included in the list. A comparison expression that includes ANY or SOME returns TRUE if the value of the data on the left satisfies simple comparison with at least one of the values in the list specified as an operand on the right. A comparison expression that includes ALL returns TRUE if the value of the data on the left satisfies simple comparison with all values in the list on the right.

When a comparison operation is performed on NULL in a comparison expression that includes ANY or SOME, UNKNOWN or TRUE is returned as a result; when a comparison operation is performed on NULL in a comparison expression that includes ALL, UNKNOWN or FALSE is returned.

expression comp_op SOME expression
expression comp_op ANY expression
expression comp_op ALL expression
  • comp_op : A comparison operator >, = or <= can be used.
  • expression (left): A single-value column, path expression (ex.: tbl_name.col_name), constant value or arithmetic function that produces a single value can be used.
  • expression (right): A column name, path expression, list (set) of constant values or subquery can be used. A list is a set represented within braces ({}). If a subquery is used, expression (left) and comparison operation on all results of the subquery execution is performed.
--creating a table

CREATE TABLE condition_tbl (id int primary key, name char(10), dept_name VARCHAR, salary INT);
INSERT INTO condition_tbl VALUES(1, 'Kim', 'devel', 4000000);
INSERT INTO condition_tbl VALUES(2, 'Moy', 'sales', 3000000);
INSERT INTO condition_tbl VALUES(3, 'Jones', 'sales', 5400000);
INSERT INTO condition_tbl VALUES(4, 'Smith', 'devel', 5500000);
INSERT INTO condition_tbl VALUES(5, 'Kim', 'account', 3800000);
INSERT INTO condition_tbl VALUES(6, 'Smith', 'devel', 2400000);
INSERT INTO condition_tbl VALUES(7, 'Brown', 'account', NULL);

--selecting rows where department is sales or devel
SELECT * FROM condition_tbl WHERE dept_name = ANY{'devel','sales'};

           id  name                  dept_name                  salary
======================================================================
            1  'Kim       '          'devel'                   4000000
            2  'Moy       '          'sales'                   3000000
            3  'Jones     '          'sales'                   5400000
            4  'Smith     '          'devel'                   5500000
            6  'Smith     '          'devel'                   2400000

--selecting rows comparing NULL value in the ALL group conditions
SELECT * FROM condition_tbl WHERE salary > ALL{3000000, 4000000, NULL};

There are no results.

--selecting rows comparing NULL value in the ANY group conditions
SELECT * FROM condition_tbl WHERE salary > ANY{3000000, 4000000, NULL};

           id  name                  dept_name                  salary
======================================================================
            1  'Kim       '          'devel'                   4000000
            3  'Jones     '          'sales'                   5400000
            4  'Smith     '          'devel'                   5500000
            5  'Kim       '          'account'                 3800000

--selecting rows where salary*0.9 is less than those salary in devel department
SELECT * FROM condition_tbl WHERE (
  (0.9 * salary) < ALL (SELECT salary FROM condition_tbl
  WHERE dept_name = 'devel')
);

           id  name                  dept_name                  salary
======================================================================
            6  'Smith     '          'devel'                   2400000

BETWEEN

The BETWEEN makes a comparison to determine whether the data value on the left exists between two data values specified on the right. It returns TRUE even when the data value on the left is the same as a boundary value of the comparison target range. If NOT comes before the BETWEEN keyword, the result of a NOT operation on the result of the BETWEEN operation is returned.

i BETWEEN g AND m and the compound condition i >= g AND i <= m have the same effect.

expression [ NOT ] BETWEEN expression AND expression
  • expression : A column name, path expression (ex.: tbl_name.col_name), constant value, arithmetic expression or aggregate function can be used. For a character string expression, the conditions are evaluated in alphabetical order. If NULL is specified for at least one of the expressions, the BETWEEN predicate returns UNKNOWN as a result.
--selecting rows where 3000000 <= salary <= 4000000
SELECT * FROM condition_tbl WHERE salary BETWEEN 3000000 AND 4000000;
SELECT * FROM condition_tbl WHERE (salary >= 3000000) AND (salary <= 4000000);

           id  name                  dept_name                  salary
======================================================================
            1  'Kim       '          'devel'                   4000000
            2  'Moy       '          'sales'                   3000000
            5  'Kim       '          'account'                 3800000

--selecting rows where salary < 3000000 or salary > 4000000
SELECT * FROM condition_tbl WHERE salary NOT BETWEEN 3000000 AND 4000000;

           id  name                  dept_name                  salary
======================================================================
            3  'Jones     '          'sales'                   5400000
            4  'Smith     '          'devel'                   5500000
            6  'Smith     '          'devel'                   2400000

--selecting rows where name starts from A to E
SELECT * FROM condition_tbl WHERE name BETWEEN 'A' AND 'E';

           id  name                  dept_name                  salary
======================================================================
            7  'Brown     '          'account'                    NULL

EXISTS

The EXISTS returns TRUE if one or more results of the execution of the subquery specified on the right exist, and returns FALSE if the result of the operation is an empty set.

EXISTS expression
  • expression : Specifies a subquery and compares to determine whether the result of the subquery execution exists. If the subquery does not produce any result, the result of the conditional expression is FALSE.
--selecting rows using EXISTS and subquery
SELECT 'raise' FROM db_root WHERE EXISTS(
SELECT * FROM condition_tbl WHERE salary < 2500000);

  'raise'
======================
  'raise'

--selecting rows using NOT EXISTS and subquery
SELECT 'raise' FROM db_root WHERE NOT EXISTS(
SELECT * FROM condition_tbl WHERE salary < 2500000);

There are no results.

IN

The IN compares to determine whether the single data value on the left is included in the list specified on the right. That is, the predicate returns TRUE if the single data value on the left is an element of the expression specified on the right. If NOT comes before the IN keyword, the result of a NOT operation on the result of the IN operation is returned.

expression [ NOT ] IN expression
  • expression (left): A single-value column, path expression (ex.: tbl_name.col_name), constant value or arithmetic function that produces a single value can be used.
  • expression (right): A column name, path expression, list (set) of constant values or subquery can be used. A list is a set represented within parentheses (()) or braces ({}). If a subquery is used, comparison with expression(left) is performed for all results of the subquery execution.
--selecting rows where department is sales or devel
SELECT * FROM condition_tbl WHERE dept_name IN {'devel','sales'};
SELECT * FROM condition_tbl WHERE dept_name = ANY{'devel','sales'};

           id  name                  dept_name                  salary
======================================================================
            1  'Kim       '          'devel'                   4000000
            2  'Moy       '          'sales'                   3000000
            3  'Jones     '          'sales'                   5400000
            4  'Smith     '          'devel'                   5500000
            6  'Smith     '          'devel'                   2400000

--selecting rows where department is neither sales nor devel
SELECT * FROM condition_tbl WHERE dept_name NOT IN {'devel','sales'};

           id  name                  dept_name                  salary
======================================================================
            5  'Kim       '          'account'                 3800000
            7  'Brown     '          'account'                    NULL

IS NULL

The IS NULL compares to determine whether the expression specified on the left is NULL, and if it is NULL, returns TRUE and it can be used in the conditional expression. If NOT comes before the NULL keyword, the result of a NOT operation on the result of the IS NULL operation is returned.

expression IS [ NOT ] NULL
  • expression : A single-value column, path expression (ex.: tbl_name.col_name), constant value or arithmetic function that produces a single value can be used.
--selecting rows where salary is NULL
SELECT * FROM condition_tbl WHERE salary IS NULL;

           id  name                  dept_name                  salary
======================================================================
            7  'Brown     '          'account'                    NULL

--selecting rows where salary is NOT NULL
SELECT * FROM condition_tbl WHERE salary IS NOT NULL;

           id  name                  dept_name                  salary
======================================================================
            1  'Kim       '          'devel'                   4000000
            2  'Moy       '          'sales'                   3000000
            3  'Jones     '          'sales'                   5400000
            4  'Smith     '          'devel'                   5500000
            5  'Kim       '          'account'                 3800000
            6  'Smith     '          'devel'                   2400000

--simple comparison operation returns NULL when operand is NULL
SELECT * FROM condition_tbl WHERE salary = NULL;

There are no results.

LIKE

The LIKE compares patterns between character string data, and returns TRUE if a character string whose pattern matches the search word is found. Pattern comparison target types are CHAR, VARCHAR and STRING. The LIKE search cannot be performed on an BIT type. If NOT comes before the LIKE keyword, the result of a NOT operation on the result of the LIKE operation is returned.

A wild card string corresponding to any character or character string can be included in the search word on the right of the LIKE operator. % (percent) and _ (underscore) can be used. .% corresponds to any character string whose length is 0 or greater, and _ corresponds to one character. An escape character is a character that is used to search for a wild card character itself, and can be specified by the user as another character (NULL, alphabet, or number whose length is 1. See below for an example of using a character string that includes wild card or escape characters.

expression [ NOT ] LIKE pattern [ ESCAPE char ]
  • expression: Specifies the data type column of the character string. Pattern comparison, which is case-sensitive, starts from the first character of the column.
  • pattern: Enters the search word. A character string with a length of 0 or greater is required. Wild card characters (% or _) can be included as the pattern of the search word. The length of the character string is 0 or greater.
  • ESCAPE char : NULL, alphabet, or number is allowed for char. If the string pattern of the search word includes "_" or "%" itself, an ESCAPE character must be specified. For example, if you want to search for the character string "10%" after specifying backslash (\) as the ESCAPE character, you must specify "10%" for pattern. If you want to search for the character string "C:\", you can specify "C:\" for pattern.

For details about character sets supported in CUBRID, see Character Strings.

Whether to detect the escape characters of the LIKE conditional expression is determined depending on the configuration of no_backslash_escapes and require_like_escape_character in the cubrid.conf file. For details, see Statement/Type-Related Parameters.

Note

  • To execute string comparison operation for data entered in the multibyte charset environment such as UTF-8, the parameter setting (single_byte_compare = yes) which compares strings by 1 byte should be added to the cubrid.conf file for a successful search result.
  • Versions after CUBRID 9.0 support Unicode charset, so the single_byte_compare parameter is no longer used.
--selection rows where name contains lower case 's', not upper case
SELECT * FROM condition_tbl WHERE name LIKE '%s%';

           id  name                  dept_name                  salary
======================================================================
            3  'Jones     '          'sales'                   5400000

--selection rows where second letter is 'O' or 'o'
SELECT * FROM condition_tbl WHERE UPPER(name) LIKE '_O%';

           id  name                  dept_name                  salary
======================================================================
            2  'Moy       '          'sales'                   3000000
            3  'Jones     '          'sales'                   5400000

--selection rows where name is 3 characters
SELECT * FROM condition_tbl WHERE name LIKE '___';

           id  name                  dept_name                  salary
======================================================================
            1  'Kim       '          'devel'                   4000000
            2  'Moy       '          'sales'                   3000000
            5  'Kim       '          'account'                 3800000

REGEXP, RLIKE

The REGEXP and RLIKE are used interchangeably; a regular expressions is a powerful way to specify a pattern for a complex search. CUBRID uses Henry Spencer's implementation of regular expressions, which conforms the POSIX 1003.2 standards. The details on regular expressions are not described in this page. For more information on regular expressions, see Henry Spencer's regex(7).

The following list describes basic characteristics of regular expressions.

  • "." matches any single character(including new-line and carriage-return).
  • "[...]" matches one of characters within square brackets. For example, "[abc]" matches "a", "b", or "c". To represent a range of characters, use a dash (-). "[a-z]" matches any alphabet letter whereas "[0-9]" matches any single number.
  • "*" matches 0 or more instances of the thing proceeding it. For example, "xabc*" matches "xab", "xabc", "xabcc", and "xabcxabc" etc. "[0-9][0-9]*" matches any numbers, and ".*" matches every string.
  • To match special characters such as "\n", "\t", "\r", and "\", some must be escaped with the backslash (\) by specifying the value of no_backslash_escapes (default: yes) to no. For details on no_backslash_escapes, see Escape Special Characters.

The difference between REGEXP and LIKE are as follows:

  • The LIKE operator succeeds only if the pattern matches the entire value.
  • The REGEXP operator succeeds if the pattern matches anywhere in the value. To match the entire value, you should use "^" at the beginning and "$" at the end.
  • The LIKE operator is case sensitive, but patterns of regular expressions in REGEXP is not case sensitive. To enable case sensitive, you should use REGEXP BINARY statement.
  • REGEXP, REGEXP BINARY works as ASCII encoding without considering the collation of operands.
SELECT ('a' collate utf8_en_ci REGEXP BINARY 'A' collate utf8_en_ci);

0

SELECT ('a' collate utf8_en_cs REGEXP BINARY 'A' collate utf8_en_cs);

0

SELECT ('a' COLLATE iso88591_bin REGEXP 'A' COLLATE iso88591_bin);

1

SELECT ('a' COLLATE iso88591_bin REGEXP BINARY 'A' COLLATE iso88591_bin);

0

In the below syntax, if expression matches pattern, 1 is returned; otherwise, 0 is returned. If either expression or pattern is NULL, NULL is returned.

The second syntax has the same meaning as the third syntax, which both syntaxes are using NOT.

expression REGEXP | RLIKE [BINARY] pattern
expression NOT REGEXP | RLIKE pattern
NOT (expression REGEXP | RLIKE pattern)
  • expression : Column or input expression
  • pattern : Pattern used in regular expressions; not case sensitive
-- When REGEXP is used in SELECT list, enclosing this with parentheses is required.
-- But used in WHERE clause, no need parentheses.
-- case insensitive, except when used with BINARY.
SELECT name FROM athlete where name REGEXP '^[a-d]';

name
======================
'Dziouba Irina'
'Dzieciol Iwona'
'Dzamalutdinov Kamil'
'Crucq Maurits'
'Crosta Daniele'
'Bukovec Brigita'
'Bukic Perica'
'Abdullayev Namik'

-- \n : match a special character, when no_backslash_escapes=no
SELECT ('new\nline' REGEXP 'new
line');

('new
line' regexp 'new
line')
=====================================
1

-- ^ : match the beginning of a string
SELECT ('cubrid dbms' REGEXP '^cub');

('cubrid dbms' regexp '^cub')
===============================
1

-- $ : match the end of a string
SELECT ('this is cubrid dbms' REGEXP 'dbms$');

('this is cubrid dbms' regexp 'dbms$')
========================================
1

--.: match any character
SELECT ('cubrid dbms' REGEXP '^c.*$');

('cubrid dbms' regexp '^c.*$')
================================
1

-- a+ : match any sequence of one or more a characters. case insensitive.
SELECT ('Aaaapricot' REGEXP '^A+pricot');

('Aaaapricot' regexp '^A+pricot')
================================
1

-- a? : match either zero or one a character.
SELECT ('Apricot' REGEXP '^Aa?pricot');

('Apricot' regexp '^Aa?pricot')
==========================
1

SELECT ('Aapricot' REGEXP '^Aa?pricot');

('Aapricot' regexp '^Aa?pricot')
===========================
1

SELECT ('Aaapricot' REGEXP '^Aa?pricot');

('Aaapricot' regexp '^Aa?pricot')
============================
0

-- (cub)* : match zero or more instances of the sequence abc.
SELECT ('cubcub' REGEXP '^(cub)*$');

('cubcub' regexp '^(cub)*$')
==========================
1

-- [a-dX], [^a-dX] : matches any character that is (or is not, if ^ is used) either a, b, c, d or X.
SELECT ('aXbc' REGEXP '^[a-dXYZ]+');

('aXbc' regexp '^[a-dXYZ]+')
==============================
1

SELECT ('strike' REGEXP '^[^a-dXYZ]+$');

('strike' regexp '^[^a-dXYZ]+$')
================================
1

Note

The following shows RegEx-Specer's license, which is library used to implement the REGEXP conditional expression.

Copyright 1992, 1993, 1994 Henry Spencer. All rights reserved.
This software is not subject to any license of the American Telephone
and Telegraph Company or of the Regents of the University of California.

Permission is granted to anyone to use this software for any purpose on
any computer system, and to alter it and redistribute it, subject
to the following restrictions:

1. The author is not responsible for the consequences of use of this
software, no matter how awful, even if they arise from flaws in it.

2. The origin of this software must not be misrepresented, either by
explicit claim or by omission. Since few users ever read sources,
credits must appear in the documentation.

3. Altered versions must be plainly marked as such, and must not be
misrepresented as being the original software. Since few users
ever read sources, credits must appear in the documentation.

4. This notice may not be removed or altered.

CASE

The CASE expression uses the SQL statement to perform an IF ... THEN statement. When a result of comparison expression specified in a WHEN clause is true, a value specified in THEN clause is returned. A value specified in an ELSE clause is returned otherwise. If no ELSE clause exists, NULL is returned.

CASE control_expression simple_when_list
[ else_clause ]
END

CASE searched_when_list
[ else_clause ]
END

simple_when :
WHEN expression THEN result

searched_when :
WHEN search_condition THEN result

else_clause :
ELSE result

result :
expression | NULL

The CASE expression must end with the END keyword. A control_expression argument and an expression argument in simple_when expression should be comparable data types. The data types of result specified in the THEN ... ELSE statement should all same, or they can be convertible to common data type.

The data type for a value returned by the CASE expression is determined based on the following rules.

  • If data types for result specified in the THEN statement are all same, a value with the data type is returned.
  • If data types can be convertible to common data type even though they are not all same, a value with the data type is returned.
  • If any of values for result is a variable length string, a value data type is a variable length string. If values for result are all a fixed length string, the longest character string or bit string is returned.
  • If any of values for result is an approximate numeric data type, a value with a numeric data type is returned. The number of digits after the decimal point is determined to display all significant figures.
--creating a table
CREATE TABLE case_tbl( a INT);
INSERT INTO case_tbl VALUES (1);
INSERT INTO case_tbl VALUES (2);
INSERT INTO case_tbl VALUES (3);
INSERT INTO case_tbl VALUES (NULL);

--case operation with a search when clause
SELECT a,
       CASE WHEN a=1 THEN 'one'
            WHEN a=2 THEN 'two'
            ELSE 'other'
       END
FROM case_tbl;

            a  case when a=1 then 'one' when a=2 then 'two' else 'other' end
===================================
            1  'one'
            2  'two'
            3  'other'
         NULL  'other'

--case operation with a simple when clause
SELECT a,
       CASE a WHEN 1 THEN 'one'
              WHEN 2 THEN 'two'
              ELSE 'other'
       END
FROM case_tbl;

            a  case a when 1 then 'one' when 2 then 'two' else 'other' end
===================================
            1  'one'
            2  'two'
            3  'other'
         NULL  'other'

--result types are converted to a single type containing all of significant figures
SELECT a,
       CASE WHEN a=1 THEN 1
            WHEN a=2 THEN 1.2345
            ELSE 1.234567890
       END
FROM case_tbl;

            a  case when a=1 then 1 when a=2 then 1.2345 else 1.234567890 end
===================================
            1  1.000000000
            2  1.234500000
            3  1.234567890
         NULL  1.234567890

--an error occurs when result types are not convertible
SELECT a,
       CASE WHEN a=1 THEN 'one'
            WHEN a=2 THEN 'two'
            ELSE 1.2345
       END
FROM case_tbl;

ERROR: Cannot coerce 'one' to type double.

Comparison Functions

COALESCE

COALESCE(expression [, expression ] ...)

The COALESCE function has more than one expression as an argument. If the first argument is non-NULL, the corresponding value is returned if it is NULL, the second argument is returned. If all expressions which have an argument are NULL, NULL is returned. Therefore, this function is generally used to replace NULL with other default value.

Parameters:expression -- Specifies more than one expression. Their types must be comparable each other.
Return type:determined with the type of the arguments

Operation is performed by converting the type of every argument into that with the highest priority. If there is an argument whose type cannot be converted, the type of every argument is converted into a VARCHAR type. The following list shows priority of conversion based on input argument type.

  • CHAR < VARCHAR
  • BIT < VARBIT
  • SHORT < INT < BIGINT < NUMERIC < FLOAT < DOUBLE
  • DATE < TIMESTAMP < DATETIME

For example, if a type of a is INT, b, BIGINT, c, SHORT, and d, FLOAT, then COALESCE (a, b, c, d) returns a FLOAT type. If a type of a is INTEGER, b, DOULBE , c, FLOAT, and d, TIMESTAMP, then COALESCE (a, b, c, d) returns a VARCHAR type.

COALESCE (a, b) works the same as the CASE expression as follows:

CASE WHEN a IS NOT NULL
THEN a
ELSE b
END

SELECT * FROM case_tbl;

            a
=============
            1
            2
            3
         NULL

--substituting a default value 10.0000 for a NULL value
SELECT a, COALESCE(a, 10.0000) FROM case_tbl;

            a  coalesce(a, 10.0000)
===================================
            1  1.0000
            2  2.0000
            3  3.0000
         NULL  10.0000

DECODE

DECODE(expression, search, result [, search, result]* [, default])

As well as a CASE expression, the DECODE function performs the same functionality as the IF ... THEN ... ELSE statement. It compares the expression argument with search argument, and returns the result corresponding to search that has the same value. It returns default if there is no search with the same value, and returns NULL if default is omitted. An expression argument and a search argument to be comparable should be same or convertible each other. The number of digits after the decimal point is determined to display all significant figures including valid number of all result.

Parameters:
  • expression,search -- expressions that are comparable with each other
  • result -- the value to be returned when matched
  • default -- the value to be retuned when no match is found
Return type:

determined with the type of result and default

DECODE(a, b, c, d, e, f) has the same meaning as the CASE expression below.

CASE WHEN a = b THEN c
WHEN a = d THEN e
ELSE f
END

SELECT * FROM case_tbl;

            a
=============
            1
            2
            3
         NULL

--Using DECODE function to compare expression and search values one by one
SELECT a, DECODE(a, 1, 'one', 2, 'two', 'other') FROM case_tbl;

            a  decode(a, 1, 'one', 2, 'two', 'other')
===================================
            1  'one'
            2  'two'
            3  'other'
         NULL  'other'

--result types are converted to a single type containing all of significant figures
SELECT a, DECODE(a, 1, 1, 2, 1.2345, 1.234567890) FROM case_tbl;

            a  decode(a, 1, 1, 2, 1.2345, 1.234567890)
===================================
            1  1.000000000
            2  1.234500000
            3  1.234567890
         NULL  1.234567890

--an error occurs when result types are not convertible
SELECT a, DECODE(a, 1, 'one', 2, 'two', 1.2345) FROM case_tbl;

ERROR: Cannot coerce 'one' to type double.

GREATEST

GREATEST(expression [, expression] ...)

The GREATEST function compares more than one expression specified as parameters and returns the greatest value. If only one expression has been specified, the expression is returned because there is no expression to be compared with.

Therefore, more than one expression that is specified as parameters must be of the type that can be compared with each other. If the types of the specified parameters are identical, so are the types of the return values; if they are different, the type of the return value becomes a convertible common data type.

That is, the GREATEST function compares the values of column 1, column 2 and column 3 in the same row and returns the greatest value while the MAX function compares the values of column in all result rows and returns the greatest value.

Parameters:expression -- Specifies more than one expression. Their types must be comparable each other. One of the arguments is NULL, NULL is returned.
Return type:same as that of the argument

The following example shows how to retrieve the number of every medals and the highest number that Korea won in the demodb database.

SELECT gold, silver , bronze, GREATEST (gold, silver, bronze)
FROM participant
WHERE nation_code = 'KOR';

         gold       silver       bronze  greatest(gold, silver, bronze)
=======================================================================
            9           12            9                              12
            8           10           10                              10
            7           15            5                              15
           12            5           12                              12
           12           10           11                              12

IF

IF(expression1, expression2, expression3)

The IF function returns expression2 if the value of the arithmetic expression specified as the first parameter is TRUE, or expression3 if the value is FALSE or NULL. expression2 and expression3 which are returned as a result must be the same or of a convertible common type. If one is explicitly NULL, the result of the function follows the type of the non-NULL parameter.

Parameters:
  • expression1 -- comparison expression
  • expression2 -- the value to be returned when expression1 is true
  • expression3 -- the value to be returned when expression1 is not true
Return type:

type of expression2 or expression3

IF(a, b, c) has the same meaning as the CASE expression in the following example:

CASE WHEN a IS TRUE THEN b
ELSE c
END

SELECT * FROM case_tbl;

            a
=============
            1
            2
            3
         NULL

--IF function returns the second expression when the first is TRUE
SELECT a, IF(a=1, 'one', 'other') FROM case_tbl;

            a   if(a=1, 'one', 'other')
===================================
            1  'one'
            2  'other'
            3  'other'
         NULL  'other'

--If function in WHERE clause
SELECT * FROM case_tbl WHERE IF(a=1, 1, 2) = 1;

            a
=============
            1

IFNULL, NVL

IFNULL(expr1, expr2)
NVL(expr1, expr2)

The IFNULL function is working like the NVL function; however, only the NVL function supports collection type as well. The IFNULL function (which has two arguments) returns expr1 if the value of the first expression is not NULL or returns expr2, otherwise.

Parameters:
  • expr1 -- expression
  • expr2 -- the value to be returned when expr1 is NULL
Return type:

determined with the type of expr1 and expr2

Operation is performed by converting the type of every argument into that with the highest priority. If there is an argument whose type cannot be converted, the type of every argument is converted into a VARCHAR type. The following list shows priority of conversion based on input argument type.

  • CHAR < VARCHAR
  • BIT < VARBIT
  • SHORT < INT < BIGINT < NUMERIC < FLOAT < DOUBLE
  • DATE < TIMESTAMP < DATETIME

For example, if a type of a is INT and b is BIGINT, then IFNULL (a, b) returns a BIGINT type. If a type of a is INTEGER and b is TIMESTAMP, then IFNULL (a, b) returns a VARCHAR type.

IFNULL(a, b) or NVL(a, b) has the same meaning as the CASE expression below.

CASE WHEN a IS NULL THEN b
ELSE a
END

SELECT * FROM case_tbl;

            a
=============
            1
            2
            3
         NULL

--returning a specific value when a is NULL
SELECT a, NVL(a, 10.0000) FROM case_tbl;

            a  nvl(a, 10.0000)
===================================
            1  1.0000
            2  2.0000
            3  3.0000
         NULL  10.0000

--IFNULL can be used instead of NVL and return values are converted to the string type
SELECT a, IFNULL(a, 'UNKNOWN') FROM case_tbl;

            a   ifnull(a, 'UNKNOWN')
===================================
            1  '1'
            2  '2'
            3  '3'
         NULL  'UNKNOWN'

ISNULL

ISNULL(expression)

The ISNULL function performs a comparison to determine if the result of the expression specified as an argument is NULL. The function returns 1 if it is NULL or 0 otherwise. You can check if a certain value is NULL. This function is working like the ISNULL expression.

Parameters:expression -- An arithmetic function that has a single-value column, path expression (ex.: tbl_name.col_name), constant value is specified.
Return type:INT 
--Using ISNULL function to select rows with NULL value
SELECT * FROM condition_tbl WHERE ISNULL(salary);

           id  name                  dept_name                  salary
======================================================================
            7  'Brown     '          'account'                    NULL

LEAST

LEAST(expression [, expression] ...)

The LEAST function compares more than one expression specified as parameters and returns the smallest value. If only one expression has been specified, the expression is returned because there is no expression to be compared with.

Therefore, more than one expression that is specified as parameters must be of the type that can be compared with each other. If the types of the specified parameters are identical, so are the types of the return values; if they are different, the type of the return value becomes a convertible common data type.

That is, the LEAST function compares the values of column 1, column 2 and column 3 in the same row and returns the smallest value while the MIN() compares the values of column in all result rows and returns the smallest value.

Parameters:expression -- Specifies more than one expression. Their types must be comparable each other. One of the arguments is NULL, NULL is returned.
Return type:same as that of the argument

The following example shows how to retrieve the number of every medals and the lowest number that Korea won in the demodb database.

SELECT gold, silver , bronze, LEAST(gold, silver, bronze) FROM participant
WHERE nation_code = 'KOR';

         gold       silver       bronze  least(gold, silver, bronze)
====================================================================
            9           12            9                            9
            8           10           10                            8
            7           15            5                            5
           12            5           12                            5
           12           10           11                           10

NULLIF

NULLIF(expr1, expr2)

The NULLIF function returns NULL if the two expressions specified as the parameters are identical, and returns the first parameter value otherwise.

Parameters:
  • expr1 -- expression to be compared with expr2
  • expr2 -- expression to be compared with expr1
Return type:

type of expr1

NULLIF (a, b) is the same of the CASE expression.

CASE
WHEN a = b THEN NULL
ELSE a
END

SELECT * FROM case_tbl;

            a
=============
            1
            2
            3
         NULL

--returning NULL value when a is 1
SELECT a, NULLIF(a, 1) FROM case_tbl;

            a  nullif(a, 1)
===========================
            1          NULL
            2             2
            3             3
         NULL          NULL

--returning NULL value when arguments are same
SELECT NULLIF (1, 1.000)  FROM db_root;

  nullif(1, 1.000)
======================
  NULL

--returning the first value when arguments are not same
SELECT NULLIF ('A', 'a')  FROM db_root;

  nullif('A', 'a')
======================
  'A'

NVL2

NVL2(expr1, expr2, expr3)

Three parameters are specified for the NVL2 function. The second expression (expr2) is returned if the first expression (expr1) is not NULL; the third expression (expr3) is returned if it is NULL.

Parameters:
  • expr1 -- expression
  • expr2 -- the value to be returned when expr1 is not NULL
  • expr3 -- the value to be returned when expr1 is NULL
Return type:

determined with the type of expr1, expr2 and expr3

Operation is performed by converting the type of every argument into that with the highest priority. If there is an argument whose type cannot be converted, the type of every argument is converted into a VARCHAR type. The following list shows priority of conversion based on input argument type.

  • CHAR < VARCHAR
  • BIT < VARBIT
  • SHORT < INT < BIGINT < NUMERIC < FLOAT < DOUBLE
  • DATE < TIMESTAMP < DATETIME

For example, if a type of a is INT, b, BIGINT, and c, SHORT, then NVL2 (a, b, c) returns a BIGINT type. If a type of a is INTEGER, b, DOUBLE, and c, TIMESTAMP, then NVL2 (a, b, c) returns a VARCHAR type.

SELECT * FROM case_tbl;

            a
=============
            1
            2
            3
         NULL

--returning a specific value of INT type
SELECT a, NVL2(a, a+1, 10.5678) FROM case_tbl;

            a  nvl2(a, a+1, 10.5678)
====================================
            1                      2
            2                      3
            3                      4
         NULL                     11