Question

假设我有一个表table1，我可以获取所有列的列表，例如double precision类型：

SELECT column_name 
FROM information_schema.columns
WHERE data_type = 'double precision' 
  AND table_name = 'table1';

如何选择这些列？

Answer 1

此问题与SELECT *类似，但*也应识别类型。

CREATE TABLE table1(ID SERIAL,col1 INT, col2 double precision,
                    col3 VARCHAR(100), col4 double precision);

INSERT INTO table1(col1,col2,col3,col4)
VALUES (1,2.0,'a',4.0), (10, 3.0, 'b', NULL);

在我看来，正确的方法是在SELECT中指定列名：

SELECT col2, col4
FROM table1;

为了使这更容易，您可以编写简单的查询，为您生成列列表：

;WITH cte(data_type, tab_name) AS
(
   SELECT 'double precision'::text, 'table1'::text
)
SELECT *
    ,FORMAT('SELECT %s FROM %s',
         COALESCE((SELECT string_agg(column_name, ',')
          FROM information_schema.columns
          WHERE data_type = c.data_type
            AND table_name = c.tab_name), '*')
          ,c.tab_name) AS result_query
FROM cte c;

的 SqlFiddleDemo

输出：

╔═══════════════════╦═══════════╦══════════════════════════════╗ ║ data_type ║ tab_name ║ result_query ║ ╠═══════════════════╬═══════════╬══════════════════════════════╣ ║ double precision ║ table1 ║ SELECT col2,col4 FROM table1 ║ ╚═══════════════════╩═══════════╩══════════════════════════════╝

当然你可以玩动态的sql甚至用函数包装它，但我不会走这条路。

PostgreSQL：选择给定类型的表列

1 个答案: