Simple Expressions

A simple expression can be a column, a pseudo-column, a constant, or a null value.

The syntax for a simple expression is as follows:

{ [database_name.]table_name.column_name
| column_name
| table_name.*
| literal
| NULL
| + simple_expr
| - simple_expr
| ~ simple_expr
| ! simple_expr
| ( expr )
| ROW ( expr [, expr ]... )
}

Common forms of simple expressions include:

• Column reference: table_name.column_name or database_name.table_name.column_name, for example, employees.salary.
• Constants: Literals such as strings and numbers, for example, 'welcome to OceanBase' and 10.
• NULL: a null value.
• Unary operators: +, -, ~ (bitwise NOT), and ! (logical NOT) act on a single simple expression.
• Parentheses expression: (expr) is used to change the operator precedence.
• Row constructor: ROW(expr [, expr ]...) is used to construct a row value.

The following are some examples of valid simple expressions:

• employees.first_name

• 'welcome to OceanBase'

• 10

• -salary