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試圖查看列中的內容我最終做了一些計數。列數爲空加外加數不爲零不加積分
該表格有3981行。
但是,已計數的列只顯示其空值和非空值的總數要低得多。
怎麼回事?
MariaDB [mydb]> select count(naf) from client where naf is not null;
+------------+
| count(naf) |
+------------+
| 83 |
+------------+
1 row in set (0.01 sec)
MariaDB [mydb]> select count(naf) from client where naf is null;
+------------+
| count(naf) |
+------------+
| 0 |
+------------+
1 row in set (0.01 sec)
MariaDB [mydb]> select count(*) from client;
+----------+
| count(*) |
+----------+
| 3981 |
+----------+
1 row in set (0.01 sec)