What does || mean in sql

The || symbol in SQL represents the string concatenation operator, which concatenates two strings into a new string. Use the following syntax: expression1 || expression2; where expression1 and expression2 are string expressions. If one of the expressions is NULL, the result will be a non-NULL expression. The || operator has lower precedence than the string comparison operators and converts numbers to strings when concatenating them.

The meaning of || in SQL

In SQL queries, the || symbol represents the string concatenation operator . It concatenates two strings into a new string.

Syntax:

<code>expression1 || expression2</code>

Where expression1 and expression2 are expressions containing string values.

Behavior:

• If both expressions are strings, the operator concatenates them.
• If one of the expressions is NULL, the result is the other expression.

Example:

<code>SELECT 'John' || ' Doe';  -- 结果：'John Doe'
SELECT NULL || ' Doe';  -- 结果：' Doe'</code>

Application scenario:

|| Operator is usually used in the following scenarios:

• Concatenate values ​​from multiple columns to create a new string.
• Add a prefix or suffix to an existing string.
• Insert blanks or other characters into the string.

Other notes: The

• || operator has lower precedence than the string comparison operator.
• When concatenating numbers, the || operator converts them to strings.

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