导入
比较缺失值
学习如何在 SQL 中比较 NULL 值。
SELECT COUNT(*) AS count_rows, COUNT(value) AS count_values FROM (VALUES (1), (null) ) AS t(value);
SELECT NULL = NULL AS equal, NULL IS NULL AS is_null;
SELECT a, b, a = b as equal, a IS DISTINCT FROM b AS is_distinct_from FROM (VALUES (1, 1), (1, 2), (1, NULL), (NULL, NULL) ) AS t(a, b);
SELECT a, b, a IS NOT DISTINCT FROM b as is_not_distinct_from, a IS DISTINCT FROM b AS is_distinct_from FROM (VALUES (1, 1), (1, 2), (1, NULL), (NULL, NULL) ) AS t(a, b);