homework-jianmu/docs-en/12-taos-sql/13-operators.md

sidebar_label	title
Operators	Operators

Arithmetic Operators

#	Operator	Data Types	Description
1	+, -	Numeric Types	Representing positive or negative numbers, unary operator
2	+, -	Numeric Types	Addition and substraction, binary operator
3	*, /	Numeric Types	Multiplication and division, binary oeprator
4	%	Numeric Types	Taking the remainder, binary operator

Bitwise Operators

#	Operator	Data Types	Description
1	&	Numeric Types	Bitewise AND, binary operator
2	|	Numeric Types	Bitewise OR, binary operator

JSON Operator

-> operator can be used to get the value of a key in a column of JSON type, the left oeprand is the column name, the right operand is a string constant. For example, col->'name' returns the value of key 'name'.

Set Operator

Set operators are used to combine the results of two queries into single result. A query including set operators is called a combined query. The number of rows in each result in a combined query must be same, and the type is determined by the first query's result, the type of the following queriess result must be able to be converted to the type of the first query's result, the conversion rule is same as CAST function.

TDengine provides 2 set operators: UNION ALL and UNION. UNION ALL combines the results without removing duplicate data. UNION combines the results and remove duplicate data rows. In single SQL statement, at most 100 set operators can be used.

Comparsion Operator

#	Operator	Data Types	Description
1	=	Except for BLOB, MEDIUMBLOB and JSON	Equal
2	<>, !=	Except for BLOB, MEDIUMBLOB, JSON and primary key of timestamp type	Not equal
3	>, <	Except for BLOB, MEDIUMBLOB and JSON	Greater than, less than
4	>=, <=	Except for BLOB, MEDIUMBLOB and JSON	Greater than or equal to, less than or equal to
5	IS [NOT] NULL	Any types	Is NULL or NOT
6	[NOT] BETWEEN AND	Except for BLOB, MEDIUMBLOB and JSON	In a value range or not
7	IN	Except for BLOB, MEDIUMBLOB, JSON and primary key of timestamp type	In a list of values or not
8	LIKE	BINARY, NCHAR and VARCHAR	Wildcard matching
9	MATCH, NMATCH	BINARY, NCHAR and VARCHAR	Regular expression matching
10	CONTAINS	JSON	If A key exists in JSON

LIKE operator uses wildcard to match a string, the rules are：

• '%' matches 0 to any number of characters; '_' matches any single ASCII character.
• _ can be used to match a _ in the string, i.e. using escape character backslash \
• Wildcard string is 100 bytes at most. Longer a wildcard string is, worse the performance of LIKE operator is.

MATCH and NMATCH operators use regular expressions to match a string, the rules are:

• Regular expressions of POSIX standard are supported.
• Only tbname, i.e. table name of sub tables, and tag columns of string types can be matched with regular expression, data columns are not supported.
• Regular expression string is 128 bytes at most, and can be adjusted by setting parameter maxRegexStringLen, which is a client side configuration and needs to restart the client to take effect.

Logical Operators

#	Operator	Data Types	Description
1	AND	BOOL	Logical AND, return TRUE if both conditions are TRUE; return FALSE if any one is FALSE.
2	OR	BOOL	Logical OR, return TRUE if any condition is TRUE; return FALSE if both are FALSE

TDengine uses shortcircut optimization when performing logical operations. For AND operator, if the first condition is evaluated to FALSE, then the second one is not evaluated. For OR operator, if the first condition is evaluated to TRUE, then the second one is not evaluated.