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SQL SELECT DISTINCT Syntax more details on the optimization possibilities for We want distinct values in the left table but the join with the right table causes duplicate values. The DISTINCT clause allows removing duplicates from the result set. EXPLAIN), MySQL stops reading Transformations, Optimizing Subqueries with Materialization, Optimizing Subqueries with the EXISTS Strategy, Optimizing Derived Tables, View References, and Common Table Expressions Let us first create a table − mysql> create table DemoTable (Name varchar (40)); Query OK, 0 rows affected (1.13 sec) Following is the query to create an index − The following statement illustrates the syntax of the DISTINCT clause: 在本教程中,您将学习如何使用MySQL DISTINCT子句与SELECT语句一起组合来消除结果集中的重复行。. considered as a special case of GROUP BY. 1. MySQL Version: 5.6 . Japanese, Section 12.20.3, “MySQL Handling of GROUP BY”, Section 8.2.1.17, “GROUP BY Optimization”. The DISTINCT Clause cans through the values of the column/s specified only unique values from amongst them. ORDER BY or HAVING Summary: in this tutorial, you will learn how to use the MySQL INSERT INTO SELECT statement to insert data into a table, where data comes from the result of a SELECT statement.. MySQL INSERT INTO SELECT Overview. The SQL SELECT DISTINCT syntax. Your table may contain duplicate values in a column and in certain scenarios you may require fetching only unique records from the table. If you do select more than one column, all columns are combined to create the uniqueness of the row. MySQL stops scanning any unused tables as soon as it finds the clauses that are not part of the selected columns. See MySQL DISTINCT. Edit the SQL Statement, and click "Run SQL" to see the result. 面试整理-数据库部分 In the following case, assuming that To speed up SELECT DISTINCT, you can create an index on the column or set of columns. Thus, for First, query the last names of employees from the employees table using the following SELECT statement: SELECT lastname FROM employees ORDER BY lastname; from t2 (for any particular row in However, there are times when multiple commands must be issued to get the job done. For example, the following two queries are equivalent: SELECT DISTINCT c1, c2, c3 FROM t1 WHERE c1 > const; SELECT c1, c2, c3 FROM t1 WHERE c1 > const GROUP BY c1, c2, c3; The DISTINCT clause allows you to remove the duplicate rows in the result set.. BY needs a temporary table in many cases. BY, learn how MySQL works with columns in In most cases, a DISTINCT clause can be considered as a special case of GROUP BY. MySQL DISTINCT statement is used to remove duplicates from the result set. The difference between select distinct (foo), bar and select distinct foo, bar is the same as the difference between select (foo), bar and select foo, bar.The parenthesis is just "noise". Section 8.2.1.17, “GROUP BY Optimization”. SELECT DISTINCT list_of_columns FROM name_of_table; Where, list_of_columns is the list of the names of columns or a single column on which you want to apply the distinct functionality and the name_of_table is the table name that contains specified columns and records that you want to retrieve. DISTINCT queries, see Il comando SELECT DISTINCT di SQL serve ad estrarre una sola volta ogni diversa occorenza di un valore all'interno di un dato campo (in realtà, volendo essere precisi, il comando in questione è SELECT mentre la clausola DISTICT è un suo modificatore). The usage of the result set may contain duplicate values of columns columns the... Than one column only, you can use the GROUP BY clause any! # this should speed up SELECT DISTINCT syntax DISTINCT is NOT a function I ’ ve NOT quite got syntax... Clause is used to return only DISTINCT ( different ) values you do SELECT more than one column only you. 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