Is there a field after select?
Yes, the field SELECT must be followed by GROUP BY. Because GROUP BY is used for grouping and SELECT is used to select the columns to be returned, the GROUP BY query must contain an aggregate function and a grouped column.
Group By field Select must be followed by?
Answer: Yes, there must be.
Expand the answer:
The GROUP BY clause is used to group records in a dataset and aggregate them together by the values of some columns. The column specified in the GROUP BY clause is called a grouped column.
The SELECT clause is used to select the column to return from the table. In a GROUP BY query, the SELECT clause must contain the following:
- Aggregation function: Used to aggregate values of grouped columns, such as SUM, COUNT, or AVG.
- Grouped column: Specifies the column to group the dataset.
If the SELECT clause does not contain an aggregate function or grouped column, the query will be invalid.
Example:
The following query groups the departments in the employee table and calculates the number of employees in each department:
<code class="sql">SELECT department, COUNT(*) AS employee_count FROM employees GROUP BY department;</code>
In this query:
-
department
is grouped column -
COUNT(*)
is an aggregate function that calculates the number of employees in each department
If there is no COUNT(*)
aggregate function or department
grouping column, the query will be invalid.
The above is the detailed content of Is there a field after select?. For more information, please follow other related articles on the PHP Chinese website!

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics

SUM in Oracle is used to calculate the sum of non-null values, while COUNT counts the number of non-null values of all data types, including duplicate values.

Aggregate functions in SQL are used to calculate and return a single value for a set of rows. Common aggregation functions include: Numeric aggregation functions: COUNT(), SUM(), AVG(), MIN(), MAX() Row set aggregation functions: GROUP_CONCAT(), FIRST(), LAST() Statistical aggregation functions: STDDEV (), VARIANCE() optional aggregate functions: COUNT(DISTINCT), TOP(N)

The SQL SUM function calculates the sum of a set of numbers by adding them together. The operation process includes: 1. Identifying the input value; 2. Looping the input value and converting it into a number; 3. Adding each number to accumulate a sum; 4. Returning the sum result.

The COUNT function in Oracle is used to count non-null values in a specified column or expression. The syntax is COUNT(DISTINCT <column_name>) or COUNT(*), which counts the number of unique values and all non-null values respectively.

MySQL's AVG() function is used to calculate the average of numeric values. It supports multiple usages, including: Calculate the average quantity of all sold products: SELECT AVG(quantity_sold) FROM sales; Calculate the average price: AVG(price); Calculate the average sales volume: AVG(quantity_sold * price). The AVG() function ignores NULL values, use IFNULL() to calculate the average of non-null values.

The SUM() function in SQL is used to calculate the sum of numeric columns. It can calculate sums based on specified columns, filters, aliases, grouping and aggregation of multiple columns, but only handles numeric values and ignores NULL values.

SC stands for SELECT COUNT in SQL, an aggregate function used to count the number of records whether or not a condition is met. SC syntax: SELECT COUNT(*) AS record_count FROM table_name WHERE condition, where COUNT(*) counts the number of all records, table_name is the table name, and condition is an optional condition (used to count the number of records that meet the condition).

Grouped data can be sorted using GROUP BY and ORDER BY: 1. GROUP BY groups data; 2. ORDER BY sorts each group of data.
