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MySQLi Articles
Page 267 of 341
MySQL count(*) from multiple tables?
To achieve this for multiple tables, use the UNION ALL.The syntax is as followsselect sum(variableName.aliasName) from ( select count(*) as yourAliasName from yourTableName1 UNION ALL select count(*) as yourAliasName from yourTableName2 ) yourVariableName;Let us implement the above syntax. Here, I am using the sample database which has more tables.The two tables we are using areuserdemowheredemoHere is the query to display all records of both the tables. The query is as follows to display records from table ‘userdemo’.mysql> select *from userdemo;The following is the output+--------+----------+------------------+ | UserId | UserName | RegisteredCourse | +--------+----------+------------------+ | 1 ...
Read MoreSelect query using MySQL IN() and avoid sorting in it
Using IN() sorts the result for the specific field. To avoid this, use ORDER BY and FIND_IN_SET() for the field.To understand the find_in_set(), let us create a table. The query to create a table is as follows −mysql> create table ProductStock -> ( -> ProductId int, -> ProductName varchar(20), -> ProductQuantity int, -> ProductPrice float -> ); Query OK, 0 rows affected (0.79 sec)Now you can insert some records in the table using insert command. The query is as follows −mysql> insert into ProductStock values(1, 'Product-101', 10, 500.56); Query OK, 1 row affected (0.20 ...
Read MoreHow to convert MySQL null to 0 using COALESCE() function?
You can use the COALESCE() function to convert MySQL null to 0SELECT COALESCE(yourColumnName, 0) AS anyAliasName FROM yourTableName;Let us first create a table. The query to create a table is as followsmysql> create table convertNullToZeroDemo -> ( -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> Name varchar(20), -> Salary int -> ); Query OK, 0 rows affected (1.28 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into convertNullToZeroDemo(Name, Salary) values('John', NULL); Query OK, 1 row affected (0.20 sec) mysql> insert into convertNullToZeroDemo(Name, Salary) values('Carol', 5610); Query OK, 1 ...
Read MoreHow to convert positive value to negative while inserting in MySQL?
Let us first create a tablemysql> create table recordsDemo -> ( -> UserId int, -> Value int -> ); Query OK, 0 rows affected (0.52 sec)Now insert some records in the table using insert command.The query is as followsmysql> insert into recordsDemo values(1, 10); Query OK, 1 row affected (0.17 sec) mysql> insert into recordsDemo values(3, 598); Query OK, 1 row affected (0.18 sec) mysql> insert into recordsDemo values(5, 786); Query OK, 1 row affected (0.25 sec) mysql> insert into recordsDemo values(7, 189); Query OK, 1 row affected (0.16 sec) mysql> insert into recordsDemo values(9, 345); ...
Read MoreExtract tuples with specified common values in another column in MySQL?
To extract tuples with specified common values, use the following syntax −SELECT DISTINCT aliasName.yourColumnName1, aliasName.yourColumnName2, aliasName1.yourColumnName 1, aliasName1.yourColumnName2 FROM yourTableName aliasName INNER JOIN yourTableName aliasName1 ON aliasName.yourColumnName1 = aliasName1.yourColumnName1 WHERE aliasName.yourColumnName2 = 'value1' AND aliasName1.yourColumnName2 = 'value2';To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table extractTuples -> ( -> Id int, -> Name varchar(20), -> Comments text -> ); Query OK, 0 rows affected (0.77 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into ...
Read MoreHow to revert rows to default column value in MySQL?
To revert rows to default column value, let us first create a demo tablemysql> create table defaultDemo -> ( -> Id int -> ); Query OK, 0 rows affected (0.48 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into defaultDemo values(10); Query OK, 1 row affected (0.25 sec) mysql> insert into defaultDemo values(20); Query OK, 1 row affected (0.13 sec) mysql> insert into defaultDemo values(30); Query OK, 1 row affected (0.14 sec) mysql> insert into defaultDemo values(40); Query OK, 1 row affected (0.11 sec) mysql> insert into defaultDemo values(80); Query OK, ...
Read MoreHow to write a MySQL “LIMIT” in SQL Server?
You need to use TOP(1) in SQL Server. The syntax is as follows −SELECT TOP(1) *FROM yourTableName WHERE yourCondition;To understand the above syntax, let us create a table. The query to create a table is as follows −create table TopDemoInSQLServer ( Id int, Name varchar(10) );The snapshot of creation of table is as follows −Insert some records in the table using insert command. The query is as follows −insert into TopDemoInSQLServer values(10, 'John'); insert into TopDemoInSQLServer values(14, 'Carol'); insert into TopDemoInSQLServer values(1, 'Sam'); insert into TopDemoInSQLServer values(11, 'Bob'); insert into TopDemoInSQLServer values(18, 'David'); insert into TopDemoInSQLServer values(20, 'Sam');The ...
Read MoreResolve the error Column count doesn’t match value count in MySQL?
This type of error occurs when number of columns does not match whenever you are inserting records in the destination table. For a demo example, let us create a tablemysql> create table errorDemo -> ( -> User_Id int NOT NULL AUTO_INCREMENT, -> User_Name varchar(20), -> PRIMARY KEY(User_Id) -> ); Query OK, 0 rows affected (0.47 sec)The error is as followsmysql> insert into errorDemo values('John'); ERROR 1136 (21S01): Column count doesn't match value count at row 1To avoid this type of error, you need to use the following syntaxinsert into yourTableName(yourColumnName1, yourColumnName2, ...N)values(yourValue1, yourValue2, ....N);Insert some ...
Read MoreHow to work with one database connection object in the entire Java-MySQL application?
Use the singleton design pattern. Here is the Java code that returns a single object −ConnectDatabase.javaimport java.sql.Connection; import java.sql.DriverManager; public class ConnectDatabase { static Connection conn = null; public static Connection getConnection() { if (conn != null) return conn; String database = "test"; String Username = "root"; String password = "123456"; return getConnection(database, Username, password); } private static Connection getConnection(String databaseName, String UserName, String password) { try { Class.forName("com.mysql.jdbc.Driver"); conn ...
Read MoreGet MySQL maximum value from 3 different columns?
To get the maximum value from three different columns, use the GREATEST() function.The syntax is as followsSELECT GREATEST(yourColumnName1, yourColumnName2, yourColumnName3) AS anyAliasName FROM yourTableName;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table MaxOfThreeColumnsDemo -> ( -> First int, -> Second int, -> Third int -> ); Query OK, 0 rows affected (0.73 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into MaxOfThreeColumnsDemo values(30, 90, 60); Query OK, 1 row affected (0.16 sec) mysql> insert into MaxOfThreeColumnsDemo values(100, ...
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