Scalar expressions

Scalar expressions are functions that calculate a single (scalar) value, even if executed on an entire column. They can be stored as a row value, as opposed to a table value which is a result set consisting of more than one column and/or row.

A scalar expression can be any one of these:

Literals

Literals are constant values.

Column references

A column reference is a column name, alias, or ordinal.

For example, in SELECT name FROM users, the column reference refers to the column titled name.

Column names may be aliased. For example in SELECT name as "First name" from users, the column reference is the alias "First name", which is quoted to maintain the case and use of space.

A column may also be referneced using an ordinal, for example in a GROUP BY or ORDER BY. In this query SELECT AVG(Salary),Team FROM nba GROUP BY 2, the ordinal 2 refers to the second column in the select list, Team.

Operators

Operators, frequently used for comparison, usually come in three forms:

Unary operator

A prefix or postfix to an expression or literals. For example, -, which is used to negate numbers.

prefix_unary_operator ::=
   + | - | NOT

postfix_unary_operator ::=
   IS NULL | IS NOT NULL

Binary operator

Two expressions or literals separated by an operator. For example, + which is used to add two numbers.

binary_operator ::=
   . | + | ^ | * | / | % | + | - | >= | <= | != | <> | ||
   | LIKE | NOT LIKE | RLIKE | NOT RLIKE | < | > | = | OR | AND

Special operators for set membership

special_operator ::=
    value_expr IN ( value_expr [, ... ] )
    | value_expr NOT IN ( value_expr [, ... ] )
    | value_expr BETWEEN value_expr AND value_expr
    | value_expr NOT BETWEEN value_expr AND value_expr

These operators return TRUE if the value_expr on the left matches the expression on the right for set membership or if the value is in-range.

Note

The data type of the left value_expr must match the type of the right side value_expr.

Comparisons

Binary operators are frequently used to compare values.

Comparison operators (< > = <= >= <> !=, IS NULL, IS NOT NULL always returns BOOL

These operators are:

Operator Name
< Smaller than
<= Smaller than or equal to
> Greater than
>= Greater than or equal to
= Equals
<> or != Not equal to
IS Identical to
IS NOT Not identical to

Note

NULL values are handled differently than other value expressions:

  • NULL is always smaller than anything, including another NULL.
  • NULL is never equal to anything, including another NULL (=). To check if a value is null, use IS NULL

Operator precedence

The table below lists the operators in decreasing order of precedence.

Precedence Operator Associativity
Highest . left
  + - (unary)  
  ^ left
  * / % left
  + - (binary) left
  || right
  BETWEEN, IN, LIKE, RLIKE  
  < > = <= >= <> !=  
  IS NULL, IS NOT NULL  
  NOT  
  AND left
Lowest OR left

Tip

Use parentheses to avoid ambiguous situations when using binary operators.

Note

The NOT variations, such as NOT BETWEEN, NOT IN, NOT LIKE, NOT RLIKE have the same precedence as their non-NOT variations.