在查詢「SELECT 1 ...」中使用「LIMIT 1」是否有意義？

是的，你可以在SELECT 1中使用LIMIT 1。

假設你正在使用SELECT 1，而你的表格有數十億筆記錄。在這種情況下，它會列印1億次。

SELECT 1的語法如下所示−

SELECT 1 FROM yourTableName;

Suppose, you are using LIMIT 1 and your table has billions of records. This case, it will print 1 only once.

The syntax of SELECT 1 with LIMIT 1 is as follows −

SELECT 1 FROM yourTableName LIMIT 1;

To understand the above syntax, let us create a table. The query to create a table is as follows −##使用插入命令在表中插入一些記錄。查詢如下 −

mysql> create table Select1AndLimit1Demo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> Name varchar(20)
   -> );
Query OK, 0 rows affected (1.99 sec)

Display all records from the table using a select statement. The query is as follows −

mysql> insert into Select1AndLimit1Demo(Name) values('John');
Query OK, 1 row affected (0.21 sec)
mysql> insert into Select1AndLimit1Demo(Name) values('Carol');
Query OK, 1 row affected (0.14 sec)
mysql> insert into Select1AndLimit1Demo(Name) values('Sam');
Query OK, 1 row affected (0.11 sec)
mysql> insert into Select1AndLimit1Demo(Name) values('Bob');
Query OK, 1 row affected (0.18 sec)
mysql> insert into Select1AndLimit1Demo(Name) values('David');
Query OK, 1 row affected (0.14 sec)
mysql> insert into Select1AndLimit1Demo(Name) values('Mike');
Query OK, 1 row affected (0.20 sec)
mysql> insert into Select1AndLimit1Demo(Name) values('Maxwell');
Query OK, 1 row affected (0.11 sec)

#輸出

mysql> select *from Select1AndLimit1Demo;

這是SELECT 1的案例。查詢如下−

+----+---------+
| Id | Name    |
+----+---------+
|  1 | John    |
|  2 | Carol   |
|  3 | Sam     |
|  4 | Bob     |
|  5 | David   |
|  6 | Mike    |
|  7 | Maxwell |
+----+---------+
7 rows in set (0.00 sec)

輸出

mysql> select 1 from Select1AndLimit1Demo;

Above, we have a table with 7 records. Therefore, the output is 7 times 1.

Let us now see the case of SELECT 1 with LIMIT 1. The query is as follows −

+---+
| 1 |
+---+
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
+---+
7 rows in set (0.00 sec)

以下是輸出的結果，只顯示值為1​​一次−

mysql> select 1 from Select1AndLimit1Demo limit 1;

上面，我們的表有7筆記錄。我們得到了1乘以1，因為我們使用了LIMIT 1。

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