SQL vs. PL/pgSQL in PostgreSQL Functions: Which Language Should I Choose?

PostgreSQL functions: SQL vs. PL/pgSQL language comparison

PostgreSQL functions can be written in SQL or the procedural language PL/pgSQL. Both languages ​​have advantages and disadvantages, and which language you choose depends on the specific needs of your function.

SQL Function

SQL functions are simpler and easier to write than PL/pgSQL functions. They are also more efficient for simple scalar queries and functions that are called only a few times per session. However, SQL functions cannot perform procedural operations such as looping or branching.

PL/pgSQL functions

PL/pgSQL functions are more powerful than SQL functions and can perform a wider range of tasks. It is a better choice for functions that require procedural operations or that are called multiple times per session. PL/pgSQL functions can also be used to define triggers and stored procedures.

The following is a summary of the main differences between SQL and PL/pgSQL functions:

特性	SQL 函数	PL/pgSQL 函数
简单性	更易编写	更复杂编写
效率	对于简单任务更高效	对于简单任务效率较低
过程操作	无法执行过程操作	可以执行过程操作
调用频率	对于每个会话仅调用几次的函数更高效	对于每个会话调用多次的函数更高效
触发器和存储过程	无法定义触发器或存储过程	可以定义触发器和存储过程

Example

The following two functions are functionally equivalent, but the SQL function is more efficient:

CREATE FUNCTION f1(istr varchar) RETURNS text AS $$
  SELECT 'hello! ' || istr;
$$ LANGUAGE SQL;

CREATE FUNCTION f2(istr varchar) RETURNS text AS $$
BEGIN
  RETURN 'hello! ' || istr;
END;
$$ LANGUAGE PL/pgSQL;

SQL function is more efficient because it does not require any procedural code to be executed. On the other hand, PL/pgSQL functions must execute BEGIN and END blocks, which adds overhead.

Conclusion

SQL and PL/pgSQL functions each have their own pros and cons. Which language you choose depends on the specific needs of your function.

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