Home >Topic List >Usage of distinct in SQL
Usage of distinct in SQL
The syntax of distinct in SQL is "SELECT DISTINCT column1, column2,...,FROM table_name;". This topic provides you with relevant articles, downloads, and course content for you to download and experience for free.
What is the usage of distinct in SQL?The syntax of distinct in SQL is "SELECT DISTINCT column1, column2,...,FROM table_name;", where column1, column2, etc. represent the column names to be queried, and table_name represents the table name to be queried. When using the DISTINCT keyword, SQL will remove duplicate rows based on the specified columns and return unique values.
How to use mysql's DISTINCTThe DISTINCT keyword of mysql has many unexpected uses. 1. It can be used when counting non-duplicate records, such as SELECTCOUNT(DISTINCTid) FROMtablename; it is to count how many records with different IDs in the talbebname table. 2. When you need to return records For specific values of different ids, you can use, for example, SELECTDISTINCTidFROMtablename; to return the specific values of different ids in the talbebname table. 3. The above situation 2 will be ambiguous when you need to return results of more than 2 columns in the mysql table, such as SELECTDISTINCTid, type
How to use distinct and group by in MySQLLet’s talk about the general conclusion first: when the semantics are the same and there is an index: both groupby and distinct can use the index, and the efficiency is the same. In the case of the same semantics and no index: distinct is more efficient than groupby. The reason is that both distinct and groupby will perform grouping operations, but groupby may perform sorting and trigger filesort, resulting in inefficient SQL execution. Based on this conclusion, you may ask: Why are groupby and distinct efficient when they have the same semantics and indexes? Under what circumstances does groupby perform sorting operations? Find answers to these two questions. Next, let’s take a look at dist
Related Resource DownloadsMore>
Related TutorialsMore>