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Found 6702 Articles for Database
556 Views
To set auto increment initial value for MySQL table, use ALTER command. The first step would bealter table yourTableName modify yourColumnName int NOT NULL AUTO_INCREMENT PRIMARY KEY, add index(yourColumnName);The second step is as followsalter table yourTableName AUTO_INCREMENT=yourStartingValue;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table setAutoIncrementDemo -> ( -> UserId int, -> UserName varchar(20) -> ); Query OK, 0 rows affected (0.75 sec)Now implement the above two steps to set auto increment initial value for MySQL table.Step 1 -The query is as followsmysql> alter ... Read More
580 Views
Let us see an example and create a table first.mysql> create table Add1ToExistingValue -> ( -> Value int -> ); Query OK, 0 rows affected (0.56 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into Add1ToExistingValue values(10); Query OK, 1 row affected (0.12 sec) mysql> insert into Add1ToExistingValue values(13); Query OK, 1 row affected (0.15 sec) mysql> insert into Add1ToExistingValue values(15); Query OK, 1 row affected (0.13 sec) mysql> insert into Add1ToExistingValue values(16); Query OK, 1 row affected (0.14 sec) mysql> insert into Add1ToExistingValue values(20); Query OK, 1 row affected (0.16 sec) mysql> insert into Add1ToExistingValue values(40); Query OK, 1 row affected (0.15 sec) mysql> insert into Add1ToExistingValue values(50); Query OK, 1 row affected (0.11 sec) mysql> insert into Add1ToExistingValue values(55); Query OK, 1 row affected (0.17 sec) mysql> insert into Add1ToExistingValue values(56); Query OK, 1 row affected (0.17 sec)Display all records from the table using select statement.The query is as followsmysql> select *from Add1ToExistingValue;The following is the output+-------+ | Value | +-------+ | 10 ... Read More
677 Views
Let us work around two cases −Case 1 − The syntax is as follows when the field is present and set to null.db.yourCollectionName.count({yourFieldName: null});Case 1 − The syntax is as follows when the field is not present and not set.db.yourCollectionName.count({yourFieldName: {$exists: false}});To understand both the above syntaxes, let us create a collection with the document. The query to create a collection with a document is as follows −> db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Larry", "EmployeeAge":null, "EmployeeSalary":18500}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a995c6cea1f28b7aa07fe") } > db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Bob", "EmployeeAge":21, "EmployeeSalary":23500}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a99836cea1f28b7aa07ff") } > db.fieldIsNullOrNotSetDemo.insertOne({"EmployeeName":"Carol", "EmployeeSalary":45500}); { ... Read More
637 Views
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 More
119 Views
To find items that do not have a certain field, use the $exists operator. The syntax is as follows −> db.yourCollectionName.find({"yourItemName":{$exists:false}}).pretty();To understand the syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.findDocumentDoNotHaveCertainFields.insertOne({"UserId":101, "UserName":"John", "UserAge":21}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a95fb6cea1f28b7aa07fb") } > db.findDocumentDoNotHaveCertainFields.insertOne({"UserName":"David", "UserAge":22, "UserFavouriteSubject":["C", "Java"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a96116cea1f28b7aa07fc") } > db.findDocumentDoNotHaveCertainFields.insertOne({"UserName":"Bob", "UserAge":24, "UserFavouriteSubject":["MongoDB", "MySQL"]}); { "acknowledged" : true, "insertedId" : ObjectId("5c8a96306cea1f28b7aa07fd") }Display all documents from a collection with the help of find() method. The ... Read More
149 Views
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 More
889 Views
PyMongo is a Python distribution containing tools for working with MongoDB. To perform regex queries with PyMongo, the syntax is as follows −db.yourCollectionName.find({'yourCollectionName':{'$regex':'^yourWords'}}).pretty();The above syntax will give all those documents that start from a specific word.To understand the syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.performRegex.insertOne({"ClientName":"Larry", "ClientFolderInformation":[ "Folder 1", "Folder 2", "Folder 3", "Folder 4", "Folder 5"], "MainFolderLocation":"/MainFolder/Details/ClientFolder" }); { "acknowledged" : true, "insertedId" : ObjectId("5c8a8b186cea1f28b7aa07f2") } > db.performRegex.insertOne({"ClientName":"Larry", "ClientFolderInformation":[ "ClientFolder 1", "ClientFolder 2", "ClientFolder 3", "ClientFolder 4", "ClientFolder 5"], ... Read More
1K+ Views
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 More
178 Views
Let us see how to loop through a stored procedure in MySQLmysql> DELIMITER // mysql> CREATE PROCEDURE do_WhileDemo(LastValue INT) -> BEGIN -> SET @loop = 0; -> REPEAT -> SET @loop= @loop+ 1; -> select @loop; -> UNTIL @loop >LastValue -> END REPEAT; -> END // Query OK, 0 rows affected (0.17 sec) mysql> DELIMITER ;Now call the stored procedure with the help of CALL command.The query is as followsmysql> call do_WhileDemo(10);The following is the output+-------+ | ... Read More
100 Views
You need to use rand() function to select random result from MySQL.The syntax is as followsselect *from yourTableName order by rand() limit 1;To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table selectRandomRecord -> ( -> StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, -> StudentName varchar(20) -> ); Query OK, 0 rows affected (0.53 sec)Insert some records in the table using insert command.The query is as followsmysql> insert into selectRandomRecord(StudentName) values('John'); Query OK, 1 row affected (0.17 sec) mysql> insert into selectRandomRecord(StudentName) values('Carol'); Query OK, ... Read More