The difference between concat function and || in oracle

CONCAT and || are both string connection functions in Oracle. The main differences are: function syntax (CONCAT with parentheses, || without), NULL processing (CONCAT returns NULL, || returns an empty string ), performance (CONCAT is slower) and usage scenarios (CONCAT is used for multi-string concatenation that may have NULL, || is used for small-string concatenation without NULL).

##The difference between CONCAT and || in Oracle

Get straight to the point: CONCAT and || are functions used for string concatenation in Oracle. The main difference is:

Function syntax:

CONCAT(str1, str2, ...)
• str1 || str2 || ...

NULL Handling:

CONCAT Returns NULL if any input string is NULL.
• || Treat NULL as an empty string.

Performance:

CONCAT is generally slower than ||.

Usage scenarios:

CONCAT:

When you need to ensure that the connected string is not Used when NULL is included.
• For situations where multiple strings need to be concatenated.

||:

Used when none of the connected strings contain NULL.
• For the case of concatenating fewer strings.

Example:

SELECT CONCAT('John', NULL, 'Smith') FROM dual; -- 返回 NULL
SELECT 'John' || NULL || 'Smith' FROM dual; -- 返回 'JohnSmith'

SELECT CONCAT('John', ' ', 'Smith') FROM dual; -- 返回 'John Smith'
SELECT 'John' || ' ' || 'Smith' FROM dual; -- 也返回 'John Smith'

Note:

|| Operator precedence is higher than CONCAT function.
• || can be used to connect different types of data such as strings, numbers or dates.
• CONCAT function is available in Oracle 8 and later.

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