Value Expressions

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Most SQL statements can contain value expressions that compute new values from data. For example, in the query SELECT ceil(price) FROM items, the expression ceil(price) computes the rounded-up value of the values from the price column.

Value expressions produce values suitable to store in a single table cell (one column of one row). They can be contrasted with table expressions, which produce results structured as a table.

The following sections provide details on each of these options.

Constants

Constant expressions represent a simple value that doesn't change. They are described further in section SQL Constants.

Column References

An expression in a query can refer to columns in the current data source in two ways:

• Using the name of the column, e.g., price in SELECT price FROM items.

  • If the name of a column is also a SQL keyword, the name must be appropriately quoted. For example: SELECT "Default" FROM configuration.
  • If the name is ambiguous (e.g., when joining across multiple tables), it is possible to disambiguate by prefixing the column name by the table name. For example, SELECT items.price FROM items.

• Using the ordinal position of the column. For example, SELECT @1 FROM items selects the first column in items.

This is a CockroachDB SQL extension.

Unary and Binary Operations

An expression prefixed by a unary operator, or two expressions separated by a binary operator, form a new expression.

CockroachDB supports the following operators:

See also this section over which data types are valid operands for each operator.

Value Comparisons

The standard operators < (smaller than), > (greater than), <= (lower than or equal to), >= (greater than or equal to), = (equals), <> and != (not equal to), IS (identical to), and IS NOT (not identical to) can be applied to any pair of values from a single data type, as well as some pairs of values from different data types.

See also this section over which data types are valid operands for each operator.

The following special rules apply:

• NULL is always ordered smaller than every other value, even itself.
• NULL is never equal to anything via =, even NULL. To check whether a value is NULL, use the IS operator or the conditional expression IFNULL(..).

Typing rule

All comparisons accept any combination of argument types and result in type BOOL.

Set Membership

Syntax:

<expr> IN <expr>
<expr> IN ( ... subquery ... )

<expr> NOT IN <expr>
<expr> NOT IN ( ... subquery ... )

Returns TRUE if and only if the value of the left operand is part of the result of evaluating the right operand.

For example:

> SELECT a IN (1, 2, 3) FROM sometable;
> SELECT a IN (SELECT * FROM allowedvalues) FROM sometable;
> SELECT ('x', 123) IN (SELECT * FROM rows);

Typing rule

IN requires its right operand to be a homogeneous tuple type and its left operand to match the tuple element type. The result has type BOOL.

String Pattern Matching

Syntax:

<expr> LIKE <expr>
<expr> ILIKE <expr>
<expr> NOT LIKE <expr>
<expr> NOT ILIKE <expr>

Evaluates both expressions as strings, then tests whether the string on the left matches the pattern given on the right. Returns TRUE if a match is found or FALSE otherwise, or the inverted value for the NOT variants.

Patterns can contain _ to match any single character, or % to match any sequence of zero or more characters. ILIKE causes the match to be tested case-insensitively.

For example:

> SELECT 'monday' LIKE '%day' AS a, 'tuesday' LIKE 'tue_day' AS b, 'wednesday' ILIKE 'W%' AS c;

+------+------+------+
|  a   |  b   |  c   |
+------+------+------+
| true | true | true |
+------+------+------+

Typing rule

The operands must be either both STRING or both BYTES. The result has type BOOL.

String Matching Using POSIX Regular Expressions

Syntax:

<expr> ~ <expr>
<expr> ~* <expr>
<expr> !~ <expr>
<expr> !~* <expr>

Evaluates both expressions as strings, then tests whether the string on the left matches the pattern given on the right. Returns TRUE if a match is found or FALSE otherwise, or the inverted value for the ! variants.

The pattern is expressed using POSIX regular expression syntax. Unlike LIKE patterns, a regular expression is allowed to match anywhere inside a string, not only at the beginning.

For example:

> SELECT 'monday' ~ 'onday' AS a, 'tuEsday' ~ 't[uU][eE]sday' AS b, 'wednesday' ~* 'W.*y' AS c;

+------+------+------+
|  a   |  b   |  c   |
+------+------+------+
| true | true | true |
+------+------+------+

Typing rule

The operands must be either both STRING or both BYTES. The result has type BOOL.

String Matching Using SQL Regular Expressions

Syntax:

<expr> SIMILAR TO <expr>
<expr> NOT SIMILAR TO <expr>

Evaluates both expressions as strings, then tests whether the string on the left matches the pattern given on the right. Returns TRUE if a match is found or FALSE otherwise, or the inverted value for the NOT variant.

The pattern is expressed using the SQL standard's definition of a regular expression. This is a mix of SQL LIKE patterns and POSIX regular expressions:

• _ and % denote any character or any string, respectively.
• . matches specifically the period character, unlike in POSIX where it is a wildcard.
• Most of the other POSIX syntax applies as usual.
• The pattern matches the entire string (as in LIKE, unlike POSIX regular expressions).

For example:

> SELECT 'monday' SIMILAR TO '_onday' AS a, 'tuEsday' SIMILAR TO 't[uU][eE]sday' AS b, 'wednesday' SIMILAR TO 'w%y' AS c;

+------+------+------+
|  a   |  b   |  c   |
+------+------+------+
| true | true | true |
+------+------+------+

Typing rule

The operands must be either both STRING or both BYTES. The result has type BOOL.

Operator Precedence

CockroachDB uses the following grouping precedence of operators in expressions:

Function Calls and SQL Special Forms

General syntax:

<name> ( <arguments...> )

A built-in function name followed by an opening parenthesis, followed by a comma-separated list of expressions, followed by a closing parenthesis.

This applies the named function to the arguments between parentheses. When the function's namespace is not prefixed, the name resolution rules determine which function is called.

See also the separate section on supported built-in functions.

In addition, the following SQL special forms are also supported:

Typing rule

In general, a function call requires the arguments to be of the types accepted by the function, and returns a value of the type determined by the function.

However, the typing of function calls is complicated by the fact SQL supports function overloading. See our blog post for more details.

Subscripted Expressions

It is possible to access one item in an array value using the [ ... ] operator.

For example, if the name a refers to an array of 10 values, a[3] will retrieve the 3rd value. The first value has index 1.

If the index is smaller or equal to 0, or larger than the size of the array, then the result of the subscripted expression is NULL.

Typing rule

The subscripted expression must have an array type; the index expression must have type INT. The result has the element type of the subscripted expression.

Conditional Expressions

Expressions can test a conditional expression and, depending on whether or which condition is satisfied, evaluate to one or more additional operands.

These expression formats share the following property: some of their operands are only evaluated if a condition is true. This matters especially when an operand would be invalid otherwise. For example, IF(a=0, 0, x/a) returns 0 if a is 0, and x/a otherwise.

IF Expressions

Syntax:

IF ( <cond>, <expr1>, <expr2> )

Evaluates <cond>, then evaluates <expr1> if the condition is true, or <expr2> otherwise.

The expression corresponding to the case when the condition is false is not evaluated.

Typing rule

The condition must have type BOOL, and the two remaining expressions must have the same type. The result has the same type as the expression that was evaluated.

Simple CASE Expressions

Syntax:

CASE <cond>
    WHEN <condval1> THEN <expr1>
  [ WHEN <condvalx> THEN <exprx> ] ...
  [ ELSE <expr2> ]
END

Evaluates <cond>, then picks the WHEN branch where <condval> is equal to <cond>, then evaluates and returns the corresponding THEN expression. If no WHEN branch matches, the ELSE expression is evaluated and returned, if any. Otherwise, NULL is returned.

Conditions and result expressions after the first match are not evaluated.

Typing rule

The condition and the WHEN expressions must have the same type. The THEN expressions and the ELSE expression, if any, must have the same type. The result has the same type as the THEN/ELSE expressions.

Searched CASE Expressions

Syntax:

CASE WHEN <cond1> THEN <expr1>
   [ WHEN <cond2> THEN <expr2> ] ...
   [ ELSE <expr> ]
END

In order, evaluates each <cond> expression; at the first <cond> expression that evaluates to TRUE, returns the result of evaluating the corresponding THEN expression. If none of the <cond> expressions evaluates to true, then evaluates and returns the value of the ELSE expression, if any, or NULL otherwise.

Conditions and result expressions after the first match are not evaluated.

Typing rule

All the WHEN expressions must have type BOOL. The THEN expressions and the ELSE expression, if any, must have the same type. The result has the same type as the THEN/ELSE expressions.

NULLIF Expressions

Syntax:

NULLIF ( <expr1>, <expr2> )

Equivalent to: IF ( <expr1> = <expr2>, NULL, <expr1> )

Typing rule

Both operands must have the same type, which is also the type of the result.

COALESCE and IFNULL Expressions

Syntax:

IFNULL ( <expr1>, <expr2> )
COALESCE ( <expr1> [, <expr2> [, <expr3> ] ...] )

COALESCE evaluates the first expression first. If its value is not NULL, its value is returned directly. Otherwise, it returns the result of applying COALESCE on the remaining expressions. If all the expressions are NULL, NULL is returned.

Arguments to the right of the first non-null argument are not evaluated.

IFNULL(a, b) is equivalent to COALESCE(a, b).

Typing rule

The operands must have the same type, which is also the type of the result.

Logical operators

The Boolean operators AND, OR and NOT are available.

Syntax:

NOT <expr>
<expr1> AND <expr2>
<expr1> OR <expr2>

AND and OR are commutative. Moreover, the input to AND and OR is not evaluated in any particular order. Some operand may not even be evaluated at all if the result can be fully ascertained using only the other operand.

Typing rule

The operands must have type BOOL. The result has type BOOL.

Aggregate Expressions

An aggregate expression has the same syntax as a function call, with a special case for COUNT:

<name> ( <arguments...> )
COUNT ( * )

The difference between aggregate expressions and function calls is that the former use aggregate functions and can only appear in the list of rendered expressions in a SELECT clause.

An aggregate expression computes a combined value, depending on which aggregate function is used, across all the rows currently selected.

Typing rule

The operand and return types are determined like for regular function calls.

Window Function Calls

A window function call has the syntax of a function call followed by an OVER clause:

<name> ( <arguments...> ) OVER <window>
<name> ( * ) OVER <window>

It represents the application of a window or aggregate function over a subset ("window") of the rows selected by a query.

Typing rule

The operand and return types are determined like for regular function calls.

Explicit Type Coercions

Syntax:

<expr> :: <type>
CAST (<expr> AS <type>)

Evaluates the expression and converts the resulting value to the specified type. An error is reported if the conversion is invalid.

For example: CAST(now() AS DATE)

Note that in many cases a type annotation is preferrable to a type coercion. See the section on type annotations below for more details.

Typing rule

The operand can have any type. The result has the type specified in the CAST expression.

As a special case, if the operand is a literal, a constant expression or a placeholder, the CAST type is used to guide the typing of the operand. See our blog post for more details.

Collation Expressions

Syntax:

<expr> COLLATE <collation>

Evaluates the expression and converts its result to a collated string with the specified collation.

For example: 'a' COLLATE de

Typing rule

The operand must have type STRING. The result has type COLLATEDSTRING.

Existence Test on the Result of Subqueries

Syntax:

EXISTS ( ... subquery ... )
NOT EXISTS ( ... subquery ... )

Evaluates the subquery and then returns TRUE or FALSE depending on whether the subquery returned any row (for EXISTS) or didn't return any row (for NOT EXISTS).

Typing rule

The operand can have any table type. The result has type BOOL.

Scalar Subqueries

Syntax:

( ... subquery ... )

Evaluates the subquery, asserts that it returns a single row and single column, and then evaluates to the value of that single cell.

For example:

> SELECT (SELECT COUNT(*) FROM users) > (SELECT COUNT(*) FROM admins);

returns TRUE if there are more rows in table users than in table admins.

Typing rule

The operand must have a table type with only one column. The result has the type of that single column.

Array Constructors

Syntax:

ARRAY[ <expr>, <expr>, ... ]

Evaluates to an array containing the specified values.

For example:

> SELECT ARRAY[1,2,3] AS a;

+---------+
|    a    |
+---------+
| {1,2,3} |
+---------+

The data type of the array is inferred from the values of the provided expressions. All the positions in the array must have the same data type.

If there are no expressions specified (empty array), or all the values are NULL, then the type of the array must be specified explicitly using a type annotation. For example:

> SELECT ARRAY[]:::int[];

Typing rule

The operands must all have the same type. The result has the array type with the operand type as element type.

Tuple Constructor

Syntax:

(<expr>, <expr>, ...)
ROW (<expr>, <expr>, ...)

Evaluates to a tuple containing the values of the provided expressions.

For example:

> SELECT ('x', 123, 12.3) AS a;

+----------------+
|       a        |
+----------------+
| ('x',123,12.3) |
+----------------+

The data type of the resulting tuple is inferred from the values. Each position in a tuple can have a distinct data type.

Typing rule

The operands can have any type. The result has a tuple type whose item types are the types of the operands.

Explicitly Typed Expressions

Syntax:

<expr>:::<type>
ANNOTATE_TYPE(<expr>, <type>)

Evaluates to the given expression, requiring the expression to have the given type. If the expression doesn't have the given type, an error is returned.

Type annotations are specially useful to guide the arithmetic on numeric values. For example:

> SELECT (1 / 0):::FLOAT; --> +Inf
> SELECT (1 / 0);         --> error "division by zero"
> SELECT (1 / 0)::FLOAT;  --> error "division by zero"

Type annotations are also different from cast expressions (see above) in that they do not cause the value to be converted. For example, now()::DATE converts the current timestamp to a date value (and discards the current time), whereas now():::DATE triggers an error message (that now() does not have type DATE).

Check our blog for more information about context-dependent typing.

Typing rule

The operand must be implicitly coercible to the given type. The result has the given type.

See Also

• Constants
• Table Expressions
• Data Types

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