如何计算表的列数

Question

例如 :

tbl_ifo

id | name  | age | gender 
----------------------------
1  | John  |  15 |  Male
2  | Maria |  18 |  Female
3  | Steph |  19 |  Female
4  | Jay   |  21 |  Male

如何使用mysql计算此表的列？

Answer 1

SELECT count(*)
FROM information_schema.columns
WHERE table_name = 'tbl_ifo'

Answer 2

我想你还需要指定数据库的名称:

SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_schema = 'SchemaNameHere'
  AND table_name = 'TableNameHere'

如果您没有指定数据库的名称,则只要它与表的名称匹配,它就有可能计算所有列.例如,你有两个数据库:DBaseA and DbaseB,在DBaseA,它有两个表:塔巴(3场),塔布(4场).而在DBaseB,它再次有两个表:塔巴(4场),TABC(4场).

如果您运行此查询:

SELECT count(*)
FROM information_schema.columns
WHERE table_name = 'TabA'

它将返回7,因为有两个表名为TabA.但通过添加另一个条件table_schema = 'SchemaNameHere':

SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_schema = 'DBaseA'
  AND table_name = 'TabA'

那么它只会返回3.

Answer 3

$cs = mysql_query("describe tbl_info");
$column_count = mysql_num_rows($cs);

要不就：

$column_count = mysql_num_rows(mysql_query("describe tbl_info"));

Answer 4

要精确计算表的列数，您可以information_schema.columns通过传递所需的数据库（架构）名称和表名称来获取表格。

参考以下代码：

SELECT count(*)
FROM information_schema.columns
WHERE table_schema = 'myDB'  
AND table_name = 'table1';