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In a MySQL schema, what is the meaning of “AUTO_INCREMENT=3”

George John
Answered on 17th Apr, 2019

In MySQL, AUTO_INCREMENT=3 tells that the inserted record will start from 3 not the default 1. Let us first create a sample table and set auto increment to 3:mysql> create table Auto_incrementDemo    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> Name varchar(20)    -> ... Read More

How to change a primary key in MySQL to auto_increment?

George John
Answered on 17th Apr, 2019

To change a primary key to auto_increment, you can use MODIFY command. Let us first create a table.mysql> create table changePrimaryKeyInAutoIncrement    -> (    -> StudentId int not null primary key,    -> StudentName varchar(100),    -> StudentAge int,    -> StudentAddress varchar(100)    -> ); Query OK, 0 ... Read More

Deleting the nth row in MySQL?

Rama Giri
Answered on 17th Apr, 2019

To delete nth row in MySQL, use DELETE statement and work with subquery. Let us first create a table:mysql> create table DemoTable1    -> (    -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> StudentName varchar(100)    -> ); Query OK, 0 rows affected (0.99 sec)Following is the ... Read More

How to convert bool to int in MySQL?

George John
Answered on 17th Apr, 2019

To convert bool to int in MySQL, you can use CAST(). Let us first create a table:mysql> create table convertBoolToIntDemo -> ( -> isYoung bool -> ); Query OK, 0 rows affected (0.69 sec)Following is the query to insert some records ... Read More

MySQL query to get the count of rows in which two or more specified values appear?

George John
Answered on 17th Apr, 2019

To get the count of rows in which two or more specified values appear, let us first create a sample table:mysql> create table specifiedValuesDemo -> ( -> Value int, -> Value2 int, -> Value3 int ... Read More

Difference between count(*) and count(columnName) in MySQL?

George John
Answered on 17th Apr, 2019

The count(*) returns all rows whether column contains null value or not while count(columnName) returns the number of rows except null rows.Let us first create a table.Following is the querymysql> create table ifNotNullDemo    -> (    -> Name varchar(20)    -> ); Query OK, 0 rows affected (0.54 sec)Following ... Read More

How to declare a variable correctly in a MySQLProcedure?

George John
Answered on 17th Apr, 2019

The variable declaration must be between BEGIN and END. Under BEGIN and END, the first statement must be declaration of variable. After that you can include insert, select, etc.Let us now see an example. Here, the variable name is “output”:mysql> DELIMITER // mysql> CREATE PROCEDURE showVariablesValue() -> ... Read More

Count value for multiple columns in MySQL?

George John
Answered on 17th Apr, 2019

To count value for multiple columns, use the CASE statement. Let us first create a table::mysql> create table countValueMultipleColumnsDemo    -> (    -> Value1 int,    -> Value2 int,    -> Value3 int    -> ); Query OK, 0 rows affected (0.62 sec)Following is the query to insert some ... Read More

Total number of fields in all tables in database?

George John
Answered on 17th Apr, 2019

To get total number of fields in all tables in database, you can use information_schema.columns along with aggregate function count(*).We are using ‘sample’ database which consists of a lot of tables with fields. Following is the query to get total number of fields in all tables in database:mysql> SELECT COUNT(*) ... Read More

Sort by character length in MySQL

George John
Answered on 17th Apr, 2019

To sort by character length in MySQL use the ORDER BY LENGTH(). Let us first create a table:mysql> create table orderingAADemo    -> (    -> Value varchar(100)    -> ); Query OK, 0 rows affected (1.30 sec)Following is the query to insert some records in the table using insert ... Read More

How to suppress MySQL stored procedure output?

George John
Answered on 17th Apr, 2019

To suppress MySQL stored procedure output, you can use variable. Let us first create a table.mysql> create table person_information    -> (    -> Id int,    -> Name varchar(20)    -> ); Query OK, 0 rows affected (0.50 sec)Following is the query to insert some records in the table ... Read More

How to add column using alter in MySQL?

George John
Answered on 17th Apr, 2019

Following is the syntax to add column using alter in MySQL:alter table yourTableName add column yourColumnName yourDataType default yourValue;Let us first create a table:mysql> create table alterTableDemo    -> (    -> Id int,    -> Name varchar(10)    -> ); Query OK, 0 rows affected (0.69 sec)Let us check ... Read More

Can we order a MySQL result with mathematical operations?

George John
Answered on 17th Apr, 2019

Yes, we can order with mathematical operations using ORDER BY clause. Let us first create a table:mysql> create table orderByMathCalculation    -> (    -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> Quantity int,    -> Price int    -> ); Query OK, 0 rows affected (0.57 sec)Following ... Read More

Resolve Unknown database in JDBC error with Java-MySQL?

George John
Answered on 17th Apr, 2019

This type of error occurs if you select any database that does not exist in MySQL. Let us first display the error of unknown database in JDBC.The Java code is as follows. Here, we have set the database as ‘onlinebookstore’, which does not exist:import java.sql.Connection; import java.sql.DriverManager; public class UnknownDatabaseDemo ... Read More

How do I INSERT INTO from one MySQL table into another table and set the value of one column?

Nishtha Thakur
Answered on 16th Apr, 2019

Let us first create a table. Following is the query −mysql> create table insertOneToAnotherTable    -> (    -> Value int    -> ); Query OK, 0 rows affected (0.60 sec)Following is the query to insert some records in the table using insert command −mysql> insert into insertOneToAnotherTable values(100); Query ... Read More

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