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
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.