计算 table 的每一列中的空值：PSQL

Question

我有一个很大的table但是作为例子我只提供其中的一小部分如下：-

col1     col2     col3     col4
           10        2       12
  13        4                11
            0        1         
            3        5      111

我知道如何在一列中查找 null 值。我想通过编写一个查询来查找每一列中有多少个空值。

提前致谢

Answer 1

您可以使用带过滤器的聚合：

select count(*) filter (where col1 is null) as col1_nulls,
       count(*) filter (where col2 is null) as col2_nulls,
       count(*) filter (where col3 is null) as col3_nulls,
       count(*) filter (where col4 is null) as col4_nulls
from the_table;

Answer 2

我认为您可以即时生成此查询。这是您可以采用的一种方法的示例：

CREATE OR REPLACE FUNCTION null_counts(tablename text)
  RETURNS SETOF jsonb LANGUAGE plpgsql AS
$func$
BEGIN
RETURN QUERY EXECUTE 'SELECT to_jsonb(t) FROM (SELECT ' || (
    SELECT string_agg('count(*) filter (where ' || a.attname::text || ' is null) as ' || a.attname || '_nulls', ',')
    FROM   pg_catalog.pg_attribute a 
    WHERE  a.attrelid = tablename::regclass
    AND    a.attnum > 0
    AND    a.attisdropped = false
    ) || ' FROM   ' || tablename::regclass || ') as t';
END
$func$; 

SELECT null_counts('your_table') AS val;

计算 table 的每一列中的空值：PSQL

Count null values in each column of a table : PSQL

postgresql

postgresql-14