sql limit 子句_SQL有子句–综合指南

柔光的暖阳◎ 2023-02-28 06:14 100阅读 0赞

sql limit 子句

Hi, folks. In this article, we will be focusing on **SQL Having Clause** in detail.

嗨伙计。 在本文中，我们将重点详细讨论**SQL具有子句** 。

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## 拥有条款的必要性 **(****The need for the Having Clause****)** ##

The Having clause adds a restriction to the type and amount of data presented by any [SQL ][SQL]code block/query. In general, the Having clause guides the [SELECT statement][] to represent only those data values that satisfy a certain condition stated by it.

Haven子句为任何[SQL][]代码块/查询提供的数据类型和数量增加了限制。 通常，Having子句指导[SELECT语句][SELECT statement]仅表示那些满足它所声明的特定条件的数据值。

Now, a question may arise in your mind that when we have the option to go for SQL WHERE clause, then why has the Having clause been introduced?

现在，您可能会想到一个问题，当我们可以选择使用SQL WHERE子句时，为什么要引入Haveing子句呢？

Well, let me answer this query of yours!

好吧，让我回答您的这个查询！

SQL WHERE clause does restrict the data values by applying a condition to the data columns. But, SQL WHERE clause does not work with [SQL Aggregate functions][].

SQL WHERE子句通过将条件应用于数据列来限制数据值。 但是，SQL WHERE子句不适用于[SQL Aggregate函数][SQL Aggregate functions] 。

This is when the Having clause came into the picture. Having clause works along with the aggregate functions to apply the conditions on the SELECT statement.

这是Haveing子句出现的时候。 Have子句与聚合函数一起将条件应用于SELECT语句。

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## SQL具有的语法 **(****Syntax of the SQL Having****)** ##

Having understood the necessity of the Having clause, let’s get started with the working and implementation of the same.

了解了Haveing子句的必要性之后，让我们开始使用该子句的工作和实现。

SELECT columns 
    from Table
    GROUP BY column
    HAVING condition;

SQL Having clause needs to be placed after the GROUP BY clause. The Having clause applies the stated condition only on the groups formed by the column’s data mentioned through the GROUP BY clause.

SQL Have子句需要放在GROUP BY子句之后。 Haven子句仅将规定的条件应用于通过GROUP BY子句提及的列数据组成的组。

Further, if we do not mention GROUP BY clause before Having clause, then Having clause works like a normal [SQL WHERE clause][].

此外，如果我们在Haveing子句之前没有提到GROUP BY子句，那么Haveing子句的工作方式类似于普通的[SQL WHERE子句][SQL WHERE clause] 。

--------------------

## SQL具有子句的示例 **(****Examples of SQL Having Clause****)** ##

Let us now understand the working of the Having clause against various examples using different conditions.

现在，让我们了解Haveing子句针对使用不同条件的各种示例的工作。

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### 具有COUNT（）函数的Haveing子句 **(****The Having clause with COUNT() function****)** ###

In the below example, we have used [count() function][count_ function] as a condition to the Having clause. So, according to it, only those data values of column ‘id’ and ‘city’ would be selected, which would be grouped by the column ‘city’ and would have satisfied the Having clause’s condition.

在下面的示例中，我们使用[count（）函数][count_ function]作为Haveing子句的条件。 因此，根据它，只会选择“ id”和“ city”列的那些数据值，这些数据值将按“ city”列分组，并且已经满足了Haveing子句的条件。

**Example:**

**例：**

select COUNT(id),city 
    from Info
    GROUP BY city
    HAVING COUNT(id) = 1;

**Output:**

**输出：**

1	Mumbai
    1	Satara
    1	USA

--------------------

### 具有SUM（）函数的子句 **(****Having clause with SUM() function****)** ###

**Example:**

**例：**

select SUM(Cost),city 
    from Info
    GROUP BY city
    HAVING SUM(Cost)>50;

**Output:**

**输出：**

97	Mumbai
    165	Pune

--------------------

### SQL具有MAX（）函数的子句 **(****SQL Having clause with MAX() function****)** ###

Here’s an article about the [max() function][max_ function], if you want to learn more about it.

如果您想了解更多有关[max（）函数的信息][max_ function] ，请[参见][max_ function]这篇文章。

**Example:**

**例：**

select MAX(Cost),city 
    from Info
    GROUP BY city
    HAVING MAX(Cost)>50;

**Output:**

**输出：**

97	Mumbai
    100	Pune

--------------------

### SQL具有AVG（）函数的子句 **(****SQL Having clause with AVG() function****)** ###

Let’s try the having clause with the [avg function][count_ function]

让我们尝试使用[avg函数][count_ function]的having子句

**Example:**

**例：**

select AVG(Cost),city 
    from Info
    GROUP BY city
    HAVING AVG(Cost)>50;

**Output:**

**输出：**

97.0000	Mumbai
    82.5000	Pune

--------------------

## 使用具有多个条件的子句 **(****Using Having Clause with Multiple Conditions****)** ##

The Having clause can be used with multiple conditions along with it using SQL AND, OR operators, etc.

Haven子句可以与多个条件一起使用，以及使用SQL AND，OR运算符等的条件。

**Example 1:**

**范例1：**

In this example, we have used SQL AND operator to combine two conditions within the Having clause.

在此示例中，我们使用SQL AND运算符将Haveing子句中的两个条件组合在一起。

select AVG(Cost),city 
    from Info
    GROUP BY city
    HAVING AVG(Cost)>50 AND AVG(Cost)<95;

**Output:**

**输出：**

82.5000	Pune

**Example 2:**

**范例2：**

Here, we have made use of SQL OR operator to combine two conditions under the Having clause.

在这里，我们利用SQL OR运算符在Haveing子句下结合了两个条件。

select AVG(Cost),city 
    from Info
    GROUP BY city
    HAVING AVG(Cost)>20 OR AVG(Cost)<95;

**Output:**

**输出：**

97.0000	Mumbai
    82.5000	Pune
    50.0000	Satara
    12.0000	USA

--------------------

## SQL具有ORDER BY子句的子句 **(****SQL Having Clause with ORDER BY Clause****)** ##

The Having clause can be associated with [SQL ORDER BY clause][] using the below command:

可以使用以下命令将Haveing子句与[SQL ORDER BY子句][SQL ORDER BY clause]关联：

select columns 
    from Table
    GROUP BY column
    HAVING condition
    ORDER BY column;

**Example:**

**例：**

select AVG(Cost),city 
    from Info
    GROUP BY city
    HAVING AVG(Cost)>20 OR AVG(Cost)<95
    ORDER BY AVG(Cost);

**Output:**

**输出：**

12.0000	USA
    50.0000	Satara
    82.5000	Pune
    97.0000	Mumbai

## 结论 **(****Conclusion****)** ##

By this, we have come to the end of this topic. Please go through [SQL JournalDev][SQL] for posts related to such topics.

至此，我们到了本主题的结尾。 请浏览[SQL JournalDev][SQL]以获取与此类主题相关的帖子。

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## 参考资料 **(****References****)** ##

*  Having Clause – [Microsoft Documentation][]
    
    有条款– [Microsoft文档][Microsoft Documentation]

> 翻译自: [https://www.journaldev.com/40737/sql-having-clause][https_www.journaldev.com_40737_sql-having-clause]

sql limit 子句

[SQL]: https://www.journaldev.com/sql
[SELECT statement]: https://www.journaldev.com/18262/sql-select
[SQL Aggregate functions]: https://www.journaldev.com/19147/sql-and-or-not-sql-logical-operators
[SQL WHERE clause]: https://www.journaldev.com/18411/sql-where-clause
[count_ function]: https://www.journaldev.com/40669/sql-sum-avg-count
[max_ function]: https://www.journaldev.com/40761/sql-min-max-functions
[SQL ORDER BY clause]: https://www.journaldev.com/18675/sql-order-by-clause
[Microsoft Documentation]: https://docs.microsoft.com/en-us/sql/t-sql/queries/select-having-transact-sql?view=sql-server-ver15
[https_www.journaldev.com_40737_sql-having-clause]: https://www.journaldev.com/40737/sql-having-clause