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Database Articles
Page 346 of 547
Using UNIQUE for varchar columns with some conditions in MySQL?
For this, you can use UNIQUE constraint on one or more columns −alter table yourTablleName add unique(yourColumnName1, yourColumnName2, ...N);Let us first create a table −mysql> create table DemoTable1598 -> ( -> EmployeeId int, -> EmployeeName varchar(20), -> EmployeeCountryName varchar(20) -> ); Query OK, 0 rows affected (0.52 sec)Here is the query to implement UNIQUE on varchar columns −mysql> alter table DemoTable1598 add unique(EmployeeName, EmployeeCountryName); Query OK, 0 rows affected (0.55 sec) Records: 0 Duplicates: 0 Warnings: 0Insert some records in the table using insert command −mysql> insert into DemoTable1598 values(101, 'Adam', 'AUS'); Query OK, 1 ...
Read MoreFix ERROR 1093 (HY000): You can't specify target table for update in FROM clause while deleting the lowest value from a MySQL column?
Let us first create a table −mysql> create table DemoTable1597 -> ( -> Marks int -> ); Query OK, 0 rows affected (0.69 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1597 values(45); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable1597 values(59); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable1597 values(43); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1597 values(85); Query OK, 1 row affected (0.17 sec) mysql> insert into DemoTable1597 values(89); Query OK, 1 row affected (0.12 sec)Display all records from the table ...
Read MoreCan we use "rank" as column name with MySQL8?
The rank is a MySQL reserved word defined in MySQL version 8.0.2. Therefore, you cannot use rank as a column name. You need to use backticks around the rank.Let us first check the MySQL version we are working on. Here, I am using MySQL version 8.0.12 −mysql> select version(); +-----------+ | version() | +-----------+ | 8.0.12 | +-----------+ 1 row in set (0.00 sec)The issues by using “rank” as column name are as follows −mysql> create table DemoTable1596 -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(20), -> rank int ...
Read MoreMySQL RegExp to fetch records with only a specific number of words
For this, use Regular Expression in MySQL as in the below syntax −select * from yourTableName where yourColumnName regexp '\land[\land ]+[ ]+[\land ]+$';The above query will work when the two words are separated by a space. Let us first create a table −mysql> create table DemoTable1412 -> ( -> Name varchar(40) -> ); Query OK, 0 rows affected (0.52 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1412 values('John Adam Carol'); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable1412 values('Mike Sam'); Query OK, 1 row affected (0.15 sec) mysql> insert ...
Read MoreCall Stored Procedures within a Stored Procedure with IF Logic?
To call stored procedures within a stored procedure, the syntax is as follows −If yourInputValue > 100 then call yourProcedureName1(); else call yourProcedureName2(); end If ; ENDLet us implement the above syntax. In order to implement the above concept, let us create a stored procedure −mysql> delimiter // mysql> create procedure Hello_Stored_Procedure() -> BEGIN -> select 'Hello World!!!'; -> END -> // Query OK, 0 rows affected (0.18 sec)The query to create the second stored procedure is as follows −mysql> create procedure Hi_Stored_Procedure() -> BEGIN -> ...
Read MoreAlternative to MySQL CASE WHEN in MySQL
Use IF() method as an alternative to CASE WHEN in MySQL. Let us first create a table −mysql> create table DemoTable1593 -> ( -> PlayerScore int -> ); Query OK, 0 rows affected (0.44 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1593 values(78); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable1593 values(0); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable1593 values(89); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable1593 values(0); Query OK, 1 row affected (0.16 sec)Display all records from the table using ...
Read MoreHow to convert varchar "time" to real time in MySQL?
For this, you can use TIME_FORMAT(). Let us first create a table −mysql> create table DemoTable1591 -> ( -> ArrivalTime varchar(20) -> ); Query OK, 0 rows affected (0.58 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1591 values('1620'); Query OK, 1 row affected (0.09 sec) mysql> insert into DemoTable1591 values('2345'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1591 values('2210'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select * from DemoTable1591;This will produce the following output −+-------------+ | ArrivalTime | +-------------+ ...
Read MoreCombine two MySQL fields and update a third one with result?
Following is the syntax to combine two fields in MySQL −alter table yourTableName add column yourColumnName dataType; update yourTableName set yourAddedColumnName =concat(yourColumnName1, ' ', yourColumnName2);Let us first create a table −mysql> create table DemoTable1590 -> ( -> FirstName varchar(20), -> LastName varchar(20) -> ); Query OK, 0 rows affected (0.57 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1590 values('Adam', 'Smith'); Query OK, 1 row affected (0.45 sec) mysql> insert into DemoTable1590 values('John', 'Doe'); Query OK, 1 row affected (0.42 sec) mysql> insert into DemoTable1590 values('David', 'Miller'); Query OK, 1 row affected ...
Read MoreCan we create a database with a numeric name with MySQL?
You cannot create database with numeric name as shown below −mysql> create database 1233;This will produce the following output −ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '1233' at line 1To create a database with numeric name, you need to use backticks around the database name −create database yourDatabaseName;Let us implement the above syntax −mysql> create database `1233`; Query OK, 1 row affected (0.20 sec)Now you can switch to the same database −mysql> use `1233`; Database changed
Read MoreHow can I see how long statements take to execute on the MySQL command line?
For every single statement on MySQL command line, it shows the exact time to execute the specific statement.Let us first create a table −mysql> create table DemoTable1589 -> ( -> EmployeeId int, -> EmployeeName varchar(20) -> ); Query OK, 0 rows affected (0.56 sec)Insert some records in the table using insert command −mysql> insert into DemoTable1589 values(101, 'Sam'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable1589 values(102, 'Bob'); Query OK, 1 row affected (0.18 sec) mysql> insert into DemoTable1589 values(103, 'David'); Query OK, 1 row affected (0.16 sec)Display all records from the table ...
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