Syntax for many statements and expressions includes the term Expression, or a term for a specific kind of expression such as TableSubquery. Expressions are allowed in these specified places within statements. Some locations allow only a specific type of expression or one with a specific property. , lists all the possible SQL expressions and indicates where they are allowed.

If not otherwise specified, an expression is permitted anywhere the word Expression appears in the syntax. This includes:

• SelectExpression
• UPDATE statement (SET portion)
• VALUES Expression
• WHERE clause

Of course, many other statements include these elements as building blocks, and so allow expressions as part of these elements. Expression Type Explanation General expressions All expressions that might result in a value of any type.

Column reference expressionColumn reference

Allowed in SelectExpressions, UPDATE statements, and the WHERE clauses of data manipulation statements.

A column-Name that references the value of the column made visible to the expression containing the Column reference.

You must qualify the column-Name by the table name or correlation name if it is ambiguous.

The qualifier of a column-Name must be the correlation name, if a correlation name is given to a table that is in a FROM clause. The table name is no longer visible as a column-Name qualifier once it has been aliased by a correlation name.

Constant expressionConstant

Most built-in data types typically have constants associated with them (as shown in ).

NULL expressionNULL

Allowed in CAST expressions or in INSERT VALUES lists and UPDATE SET clauses. Using it in a CAST expression gives it a specific data type.

NULL is an untyped constant representing the unknown value.

Dynamic parameter expressionDynamic parameter

Allowed anywhere in an expression where the data type can be easily deduced. See .

A dynamic parameter is a parameter to an SQL statement for which the value is not specified when the statement is created. Instead, the statement has a question mark (?) as a placeholder for each dynamic parameter. See .

Dynamic parameters are permitted only in prepared statements. You must specify values for them before the prepared statement is executed. The values specified must match the types expected.

CAST expressionCAST expression

Lets you specify the type of NULL or of a dynamic parameter or convert a value to another type. See .

Scalar subquery expressionscalar subquery

Subquery that returns a single row with a single column. See .

Table subquery expressiontable subquery

Allowed as a tableExpression in a FROM clause and with EXISTS, IN, and quantified comparisons.

Subquery that returns more than one column and more than one row. See TableSubquery.

Conditional expressionConditional expression

A conditional expression chooses an expression to evaluate based on a boolean test. Boolean expressions Expressions that result in boolean values. Most general expressions can result in boolean values.

Boolean expressions commonly used in a WHERE clause are made of operands operated on by SQL operators. See .

Numeric expressionsNumeric expressions Expressions that result in numeric values. Most of the general expressions can result in numeric values.

Numeric values have one of the following types:

SMALLINT, INTEGER, BIGINT, REAL, DOUBLE PRECISION, DECIMAL.

+ -, *, /, unary + and - expressions+, -, *, /, unary + and - expressions

+, -, *, /, unary + and -

Evaluate the expected math operation on the operands. If both operands are the same type, the result type is not promoted, so the division operator on integers results in an integer that is the truncation of the actual numeric result. When types are mixed, they are promoted as described in .

Unary + is a noop (i.e., +4 is the same as 4). Unary - is the same as multiplying the value by -1, effectively changing its sign.

AVG

Returns the average of a set of numeric values.

SUM

Returns the sum of a set of numeric values.

LENGTH functionLENGTH

Returns the number of characters in a character or bit string. See .

LOWER

See .

COUNT

Returns the count of a set of values. See , . Character expressionsCharacter expressions Expressions that result in a CHAR or VARCHAR value. Most general expressions can result in a CHAR or VARCHAR value.

String expressionswith wildcardsA CHAR or VARCHAR value that uses wildcards.

Used in a LIKE pattern.

The wildcards % and _ make a character string a pattern against which the LIKE operator can look for a match.

Concatenation functionas expressionConcatenation expression

In a concatenation expression, the concatenation operator, "||", concatenates its right operand to the end of its left operand. Operates on character and bit strings. See .

Built-in string functions

The built-in string functions act on a String and return a string. See , , , , and

USER functions

User functions return information about the current user as a String. See , , and Date/time expressionsDate/time expressions A date/time expression results in a DATE, TIME, or TIMESTAMP value. Most of the general expressions can result in a date/time value.

CURRENT_DATE functionas expressionCURRENT_DATE

Returns the current date. See .

CURRENT_TIME functionas expressionCURRENT_TIME

Returns the current time. See .

CURRENT_TIMESTAMP functionexpressionCURRENT_TIMESTAMP

Returns the current timestamp. See .