doesn't exist in table 't_index_drop' 如果删除字段,索引也会自动删除。 mysql> alter table t_index_drop add index idx_age(age); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show create table t_index_drop \G *** 1. row *** Table: t_...
SELECT COUNT(column_name) FROM table_name; Run code Powered By Variations of the syntax achieve different goals. The COUNT(*) syntax allows us to count the number of rows in a table The COUNT(DISTINCT column) syntax allows us to count the number of distinct values in a column The ...
The output is below. The first two columns count 28 rows, whereas the 3rdcolumn using DISTINCT counts 10 rows. This is 10 because column ProductName has only 10 unique values and the rest are duplicates. There is one more argument using which we can get the total number of rows in a t...
Major importance of SQL Constraints: It creates a relationship between the tables in a database. Maintains consistency in the tables. It will prevent NULL values and duplicates. It has predefined rules for the tables. Learn SQL from Scratch: Build a Rock-Solid Data Foundation Unlock the ...
DISTINCT With COUNT We can use SQLDISTINCTwith theCOUNT()function to count the number of unique rows. Let's look at an example. -- count the unique countries where customers are fromSELECTCOUNT(DISTINCTcountry)FROMCustomers; Run Code
SELECT object_schema_name(Object_ID)+'.'+object_name(Object_ID) as tableName, count(*) as Similar, ColumnList as TheColumn, max(name)+', '+min(name) as duplicates FROM (SELECT Object_ID, name, stuff (--get a list of columns (SELECT ', ' + col_name(sc.Object_Id, sc.Column_...
Find the number of products wherePriceis higher than 20: SELECTCOUNT(ProductID) FROMProducts WHEREPrice >20; Try it Yourself » Ignore Duplicates You can ignore duplicates by using theDISTINCTkeyword in theCOUNT()function. IfDISTINCTis specified, rows with the same value for the specified colu...
mysql> insert into employees -> (name, hire_date, birth_date, email, phone_number, dept_id) -> ( -> select name, hire_date, birth_date, email, phone_number, dept_id -> from employees -> where name='张三' -> ); Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: ...
In this example, we grouped the Name, Department and counted the number of records of each record. If the count of any record is greater than one, we return the name, Department and count of that record. Using Self Joins We can also join the table with itself to find the duplicate rec...
SQL Server : find duplicates in ntext columnThis is a bit tricky, because as you write, it's...