A comprehensive guide to SQL queries

Complete list of SQL query statement commands, specific code examples are required

SQL (Structured Query Language) is a standard programming language used to manage relational databases. It can use various query statements to extract the required data to operate the database. In this article, we will provide you with some commonly used SQL query statements and attach specific code examples. Let’s find out.

1. SELECT statement: used to select data from a database table.

   • Query all data: SELECT * FROM table_name;
   • Query the data of specified columns: SELECT column1, column2 FROM table_name;
   • Query with conditions: SELECT * FROM table_name WHERE condition;

2. INSERT statement: used to insert new data into the database table.

   • Insert a single piece of data: INSERT INTO table_name (column1, column2) VALUES (value1, value2);
   • Insert multiple pieces of data: INSERT INTO table_name (column1, column2) VALUES (value1 , value2), (value3, value4);

3. UPDATE statement: used to update data in the database table.

   • Update the data of a single column: UPDATE table_name SET column1 = value1 WHERE condition;
   • Update the data of multiple columns: UPDATE table_name SET column1 = value1, column2 = value2 WHERE condition;

4. DELETE statement: used to delete data from the database table.

   • Delete all data: DELETE FROM table_name;
   • Delete conditional data: DELETE FROM table_name WHERE condition;

5. SELECT DISTINCT statement: used to retrieve unique and non-duplicate values.

   • Query the only unique column: SELECT DISTINCT column_name FROM table_name;

6. ORDER BY statement: used to sort the results according to the specified column .

   • Sort in ascending order: SELECT column1, column2 FROM table_name ORDER BY column1 ASC;
   • Sort in descending order: SELECT column1, column2 FROM table_name ORDER BY column1 DESC;

7. GROUP BY statement: used to group rows with the same value and perform aggregate calculations on them.

   • Group and calculate the total: SELECT column1, COUNT(column2) FROM table_name GROUP BY column1;

8. HAVING statement: used in GROUP BY Based on the statement, further conditional filtering is added.

   • Use HAVING to filter the grouped data: SELECT column1, COUNT(column2) FROM table_name GROUP BY column1 HAVING COUNT(column2) > value;

9. JOIN statement: used to jointly query data from multiple tables based on the relationship between tables.

   • Inner join: SELECT column1, column2 FROM table1 INNER JOIN table2 ON table1.column_name = table2.column_name;
   • Left join: SELECT column1, column2 FROM table1 LEFT JOIN table2 ON table1 .column_name = table2.column_name;
   • Right join: SELECT column1, column2 FROM table1 RIGHT JOIN table2 ON table1.column_name = table2.column_name;

10. EXISTS Statement: Used to check whether the result of the subquery exists.

    • Use EXISTS to check whether the subquery has results: SELECT column1 FROM table_name WHERE EXISTS (SELECT column2 FROM table_name2 WHERE condition);

The above is Commonly used SQL query statements and code examples. By mastering these commonly used statements, you will be able to operate the database more flexibly. Hope this article helps you!

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