In order to know the last MySQL error, you can use SHOW command −SHOW ERRORS;Or you can use another syntax −SHOW WARNINGS;Here, we are creating a table that displays an error and then we will find out how to know the last MySQL error. Here, the error occurs because we have intentionally written incorrect create table statement −mysql> create table DemoTable(Id int); 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 'create table DemoTable(Id int)' at line 1Following is the query to ... Read More

To create database only once, use the below syntax.CREATE DATABASE IF NOT EXISTS yourDatabaseName;To create table only once, use the below syntax −CREATE TABLE IF NOT EXISTS yourTableName (    yourColumnName yourDatatype,    .    .    .    N );Let us implement both the above syntaxes to create database and table only once if does not already exist −mysql> CREATE DATABASE IF NOT EXISTS login; Query OK, 1 row affected (0.23 sec)Above query creates a database successfully.Following is the query to create a table −mysql> CREATE TABLE IF NOT EXISTS DemoTable (    Id int ); Query OK, 0 rows affected (0.56 sec)Above query creates a table successfully.

You can use IF in stored procedure and IF() in select statement as well.IF() in select statementIF() in select statement mysql> select if(0=0, 'Hello MySQL', 'condition is wrong');This will produce the following output −+------------------------------------------------------+ | if('test'='test', 'Hello MySQL', 'condition is wrong') | +------------------------------------------------------+ | Hello MySQL | +------------------------------------------------------+ 1 row in set (0.00 sec)The second case if your condition ... Read More

To match underscore in a MySQL string, you can use the below syntax −select *from yourTableName where yourColumnName LIKE '%\_%';Let us first create a table −mysql> create table DemoTable (    ClientId varchar(200) ); Query OK, 0 rows affected (0.79 sec)Insert some records in the table using insert command −mysql> insert into DemoTable values('CLI_101'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('CLI1110'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable values('_CLI102'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values('CLI103_'); Query OK, 1 row affected (0.12 sec) mysql> insert into ... Read More

To check this, you can use SHOW command. The syntax is as follows −show grants\GLet us implement the above syntax to display the permissions you have −mysql> SHOW GRANTS\GThis will produce the following output −*************************** 1. row *************************** Grants for root@%: GRANT SELECT, INSERT, UPDATE, DELETE, CREATE, DROP, RELOAD, SHUTDOWN, PROCESS, FILE, REFERENCES, INDEX, ALTER, SHOW DATABASES, SUPER, CREATE TEMPORARY TABLES, LOCK TABLES, EXECUTE, REPLICATION SLAVE, REPLICATION CLIENT, CREATE VIEW, SHOW VIEW, CREATE ROUTINE, ALTER ROUTINE, CREATE USER, EVENT, TRIGGER, CREATE TABLESPACE, CREATE ROLE, DROP ROLE ON *.* TO `root`@`%` WITH GRANT OPTION *************************** 2. row *************************** Grants for root@%: ... Read More

In order to order by 0 first and then largest, you can use the below syntax −select *from yourTableName order by yourColumnName=0 DESC, yourColumnName DESC;Let us first create a table −mysql> create table DemoTable (    Value int ); Query OK, 0 rows affected (0.65 sec)Insert records in the table using insert command −mysql> insert into DemoTable values(90); Query OK, 1 row affected (0.23 sec) mysql> insert into DemoTable values(0); Query OK, 1 row affected (0.11 sec) mysql> insert into DemoTable values(20); Query OK, 1 row affected (0.12 sec) mysql> insert into DemoTable values(0); Query OK, 1 row affected (0.12 ... Read More

Let us first create a table −mysql> create table DemoTable (    UserId int,    UserName varchar(10),    UserAge int ); Query OK, 0 rows affected (0.73 sec)Insert records in the table using insert command −mysql> insert into DemoTable values(101, 'Chris', 23); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable values(102, 'Robert', 33); Query OK, 1 row affected (0.26 sec) mysql> insert into DemoTable values(103, 'David', 25); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values(104, 'Carol', 35); Query OK, 1 row affected (0.24 sec) mysql> insert into DemoTable values(105, 'Bob', 29); Query OK, ... Read More

Use MySQL JOIN to select MySQL rows where column contains same data in more than one record. Let us first create a table −mysql> create table DemoTable (    UserId int,    UserName varchar(20) ); Query OK, 0 rows affected (0.54 sec)Insert records in the table using insert command −mysql> insert into DemoTable values(10, 'John'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(11, 'Sam'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable values(12, 'Larry'); Query OK, 1 row affected (0.16 sec) mysql> insert into DemoTable values(13, 'David'); Query OK, 1 row affected (0.17 ... Read More

You can use INFORMATION_SCHEMA.TABLES and AVG_ROW_LENGTH to query average row length in MySQL −SELECT AVG_ROW_LENGTH FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = ‘yourTableName’;Let us first create a table −mysql> create table DemoTable (    StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    StudentName varchar(100) ); Query OK, 0 rows affected (0.90 sec)Insert records in the table using insert command −mysql> insert into DemoTable(StudentName) values('John'); Query OK, 1 row affected (0.15 sec) mysql> insert into DemoTable(StudentName) values('Larry'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable(StudentName) values('Sam'); Query OK, 1 row affected (0.14 sec) mysql> insert into DemoTable(StudentName) values('Mike'); Query OK, ... Read More

To prevent duplicate entry, add constraint UNIQUE. Let us first create a table −mysql> create table DemoTable (    Id int,    Name varchar(100) ); Query OK, 0 rows affected (0.79 sec)Here is the query to prevent MySQL double insert using UNIQUE −mysql> alter table DemoTable add constraint id_NameUnKey UNIQUE(Id, Name); Query OK, 0 rows affected (0.82 sec) Records: 0 Duplicates: 0 Warnings: 0Insert records in the table using insert command. When we will try to the same record again, then the “Duplicate entry” error will be visible −mysql> insert into DemoTable values(11, 'John'); Query OK, 1 row affected (0.18 ... Read More