To find/replace string in fields, the syntax is as follows −update yourTableName set yourColumnName =REPLACE(yourColumnName, yourOldValue, yourNewValue);To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table FindReplaceDemo    -> (    -> FileId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> FileDirectory text    -> ); Query OK, 0 rows affected (0.92 sec)Now you can insert some records in the table using insert command. The query is as follows −mysql> insert into FindReplaceDemo(FileDirectory) values('C://User//MySQL'); Query OK, 1 row affected (0.19 sec) mysql> insert into FindReplaceDemo(FileDirectory) values('D://WebsiteImage//image1.jpg'); Query OK, ... Read More

Adding an index on column of int type is a good choice to run your query faster whenever your table has lots of records.If your table has less records then it is not a good choice to use index on column of int type.To understand the concept, let us create a table. The query to create a table is as follows −mysql> create table indexOnIntColumnDemo    -> (    -> UserId int,    -> UserName varchar(20),    -> UserAge int,    -> INDEX(UserId)    -> ); Query OK, 0 rows affected (0.85 sec)Now check the description of table −mysql> desc ... Read More

To convert ObjectId to string, use the $toString in MongoDB. To understand the above concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.objectidToStringDemo.insertOne({"UserName":"John"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b80036de59bd9de0639d") } > db.objectidToStringDemo.insertOne({"UserName":"Chris"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b80436de59bd9de0639e") } > db.objectidToStringDemo.insertOne({"UserName":"Larry"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b80936de59bd9de0639f") } > db.objectidToStringDemo.insertOne({"UserName":"Robert"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b81836de59bd9de063a0") }Display all documents from a collection with the help of find() method. The query is as follows −> ... Read More

You can use DROP INDEX for this. The syntax is as follows −alter table yourTablename drop index yourUniqueName;To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table removeUniquenessConstraint    -> (    -> Id int,    -> Name varchar(100),    -> Age int,    -> isGreaterThan18 bool,    -> UNIQUE(Id, isGreaterThan18)    -> ); Query OK, 0 rows affected (0.69 sec)Now check the details of table with the help of SHOW CREATE command. The query is as follows −mysql> show create table removeUniquenessConstraint;Here is the output −+----------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | ... Read More

Let us first create a demo table −mysql> create table BulkChangeDemo    -> (    -> CustomerId int NOT NULL AUTO_INCREMENT PRIMARY KEY,    -> CustomerName varchar(20),    -> isEducated boolean    -> ); Query OK, 0 rows affected (1.47 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into BulkChangeDemo(CustomerName, isEducated) values('Larry', true); Query OK, 1 row affected (0.09 sec) mysql> insert into BulkChangeDemo(CustomerName, isEducated) values('John', false); Query OK, 1 row affected (0.16 sec) mysql> insert into BulkChangeDemo(CustomerName, isEducated) values('Carol', false); Query OK, 1 row affected (0.25 sec) mysql> insert into BulkChangeDemo(CustomerName, ... Read More

To hide _id from aggregation, use the below syntax −db.yourCollectionName.aggregate(    {$project : {       _id : 0 ,       yourIncludeFieldName:1,       yourIncludeFieldName:1    }} ).pretty();To understand the above syntax, let us create a collection with the document. The query to create a collection with a document is as follows −> db.hideidDemo.insertOne({"UserName":"Larry", "UserAge":23, "UserCountryName":"US"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b02336de59bd9de06392") } > db.hideidDemo.insertOne({"UserName":"Chris", "UserAge":21, "UserCountryName":"AUS"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b03036de59bd9de06393") } > db.hideidDemo.insertOne({"UserName":"Robert", "UserAge":26, "UserCountryName":"UK"}); {    "acknowledged" : true,    "insertedId" : ObjectId("5c92b04036de59bd9de06394") }Display all documents ... Read More

You can use ORDER BY RIGHT() to ORDER BY last 2 character string.The syntax is as followsselect yourColumnName from yourTableName ORDER BY RIGHT(yourColumnName , 2);To understand the above syntax, let us create a table. The query to create a table is as followsmysql> create table OrderByLast2CharactersDemo    -> (    -> CustomerId varchar(20),    -> CustomerName varchar(20)    -> ); Query OK, 0 rows affected (0.58 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into OrderByLast2CharactersDemo(CustomerId, CustomerName) values('John-98', 'John'); Query OK, 1 row affected (0.20 sec) mysql> insert into OrderByLast2CharactersDemo(CustomerId, CustomerName) values('Carol-91', ... Read More

You can verify SET FOREIGN KEY CHECKS is set to = 1 or not with the help of variable@@foreign_key_checks;The syntax is as follows −select @@foreign_key_checks;You can use SHOW VARIABLES command. The syntax is as follows −show variables like 'foreign%';Now you can implement both the syntaxes.Case 1 − Using variable @@foreign_key_checks.The query is as follows −mysql> SELECT @@foreign_key_checks; Here is the output −+----------------------+ | @@foreign_key_checks | +----------------------+ | 1 | +----------------------+ 1 row in set (0.00 sec)Case 2 − Using SHOW commandThe ... Read More

Yes, to query for a field in an object in the array with MongoDB, use the following syntax −db.yourCollectionName.find({"yourOuterFieldName": { $elemMatch: { "yourInnerFieldName": "yourValue" } } } ).pretty();To understand the above concept, let us create a collection with the document. The query to create a collection with a document is as follows −> db.objectInAnArrayDemo.insertOne({ "StudentDetails": [{    "StudentName": "John", "StudentMessage": "Hi"}, {"StudentName": "Larry", "StudentMessage": "Hello"}]}) {    "acknowledged" : true,    "insertedId" : ObjectId("5c92635d36de59bd9de06381") } > db.objectInAnArrayDemo.insertOne({ "StudentDetails": [{    "StudentName": "Carol", "StudentMessage": "Hello"}, {"StudentName": "David", "StudentMessage": "Good Morning"}]}) {    "acknowledged" : true,    "insertedId" : ObjectId("5c92637936de59bd9de06382") }Display all documents ... Read More

Ampersands work in Oracle. To work it in MySQL, use @ as shown in the following syntax −SET @yourVariableName1 = yourValue, @yourVariableName2 = yourValue, @yourVariableName3 =yourValue, .........N; insert into yourTableName values(@yourVariableName1, @yourVariableName2, @yourVariableName3, ........N);To understand the above syntax, let us create a table. The query to create a table is as follows −mysql> create table Student_Information    -> (    -> StudentId int,    -> StudentName varchar(100),    -> StudentAge int,    -> StudentMarks int,    -> StudentCountryName varchar(10)    -> ); Query OK, 0 rows affected (0.75 sec)Here is the query with values prepended by @. Insert some records ... Read More