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Database Articles
Page 133 of 546
MongoDB $push in nested array?
Here, $push can be used to add new documents in nested array. To understand the above $push concept, let us create a collection with nested array document. The query to create a collection with document is as follows:>db.nestedArrayDemo.insertOne({"EmployeeName":"Larry", "EmployeeSalary":9000, "EmployeeDetails": [{"EmployeeDOB":new Date('1990-01-21'), "EmployeeDepartment":"ComputerScience", "EmployeeProject": [{"Technology":"C", "Duration":6}, {"Technology":"Java", "Duration":7}]}]});The following is the output:{ "acknowledged" : true, "insertedId" : ObjectId("5c6d73090c3d5054b766a76e") }Now you can display documents from a collection with the help of find() method. The query is as follows:> db.nestedArrayDemo.find().pretty();The following is the output:{ "_id" : ObjectId("5c6d73090c3d5054b766a76e"), "EmployeeName" : "Larry", "EmployeeSalary" : 9000, "EmployeeDetails" ...
Read MoreGet a list of Foreign Key constraints in MySQL
Let’s say we have a database “business” with number of tables. If you want to show only foreign key constraints, then use the following query −mysql> select * −> from information_schema.referential_constraints −> where constraint_schema = 'business';The following is the output displaying only foreign key constraints −+--------------------+-------------------+--------------------------+---------------------------+--------------------------+------------------------+--------------+-------------+-------------+-------------------+-----------------------+ | CONSTRAINT_CATALOG | CONSTRAINT_SCHEMA | CONSTRAINT_NAME | UNIQUE_CONSTRAINT_CATALOG | UNIQUE_CONSTRAINT_SCHEMA | UNIQUE_CONSTRAINT_NAME | MATCH_OPTION | UPDATE_RULE | DELETE_RULE | TABLE_NAME | REFERENCED_TABLE_NAME | +--------------------+-------------------+--------------------------+---------------------------+--------------------------+------------------------+--------------+-------------+-------------+-------------------+-----------------------+ | def | business | ConstChild ...
Read MoreInsert NULL value into INT column in MySQL?
You can insert NULL value into an int column with a condition i.e. the column must not have NOT NULL constraints. The syntax is as follows.INSERT INTO yourTableName(yourColumnName) values(NULL);To understand the above syntax, let us first create a table. The query to create a table is as follows.mysql> create table InsertNullDemo -> ( -> StudentId int, -> StudentName varchar(100), -> StudentAge int -> ); Query OK, 0 rows affected (0.53 sec)Here is the query to insert NULL whenever you do not pass any value for column. Here this column is StudentAge. MySQL inserts null value by default. The query to ...
Read MoreMySQL sort string number?
To sort string number, use the CAST() function from MySQL. The syntax is as follows −SELECT *FROM yourTableName ORDER BY (yourColumnName as Decimal(integerValue, integerValueAfterDecimalPoint)) desc;To understand the above syntax, let us first create a table. The query to create a table is as follows −mysql> create table SortingStringDemo -> ( -> Amount varchar(10) -> ); Query OK, 0 rows affected (0.91 sec)Insert some records in the table using insert command. The query is as follows.mysql> insert into SortingStringDemo values('12.34'); Query OK, 1 row affected (0.21 sec) mysql> insert into SortingStringDemo values('124.50'); Query OK, 1 row affected (0.56 sec) ...
Read MoreMySQL query to select records with a particular date?
You can use DATE() from MySQL to select records with a particular date. The syntax is as follows.SELECT *from yourTableName WHERE DATE(yourDateColumnName)=’anyDate’;To understand the above syntax, let us first create a table. The query to create a table is as follows.mysql> create table AllRecordsFromadate -> ( -> Id int, -> Name varchar(100), -> Age int, -> AdmissionDate datetime -> ); Query OK, 0 rows affected (0.53 sec)Insert some records in the table using insert command. The query to insert records is as follows.mysql> insert into AllRecordsFromadate values(101, 'John', 23, '2018-10-13'); Query OK, 1 row affected (0.18 sec) mysql> insert ...
Read MoreHow to add columns at specific position in existing table in MySQL?
To add columns at a specific position in existing table, use after command. The syntax is as follows −ALTER TABLE yourTableName ADD COLUMN yourColumnName data type AFTER yourExistingColumnName;To understand the above syntax, let us first create a table. The query to create a table is as follows.mysql> create table changeColumnPosition -> ( -> Id_Position1 int, -> Name_Position2 varchar(100), -> Address_Position4 varchar(200) -> ); Query OK, 0 rows affected (0.53 sec)Now you can check the description of existing table using desc command. The syntax is as follows −desc yourTableName;The following is the query to check the description.mysql> desc changeColumnPosition;The following is ...
Read MoreChange the Auto Increment counter in MySQL?
In MySQL, auto increment counter starts from 0 by default, but if you want the auto increment to start from another number, use the below syntax.ALTER TABLE yourTable auto_increment=yourIntegerNumber;To understand the above syntax, let us first create a table. The query to create a table is as follows.mysql> create table startAutoIncrement -> ( -> Counter int auto_increment , -> primary key(Counter) -> ); Query OK, 0 rows affected (0.90 sec)Implement the above syntax to begin auto increment from 20. The query is as follows.mysql> alter table startAutoIncrement auto_increment=20; Query OK, 0 rows affected (0.30 sec) Records: 0 Duplicates: 0 Warnings: ...
Read MoreIs there any whoami function or command in MySQL like UNIX?
There is no whoami function in MySQL. The whoami can be used to know the current user in UNIX. Use user() or current_user() function from MySQL for the same purpose.The following is the output.+-----------+ | version() | +-----------+ | 8.0.12 | +-----------+ 1 row in set (0.00 sec)Case 1 −Using CURRENT_USER() function.The query to know the current user is as follows.mysql> select current_user();The following is the output.+----------------+ | current_user() | +----------------+ | root@% | +----------------+ 1 row in set (0.00 sec)Case 2 − Using USER() function.The query is as follows −mysql> select user();The following is ...
Read MoreSelect values that meet different conditions on different rows in MySQL?
You can select values that meet different conditions on different rows using IN() and GROUP BY. The syntax is as follows −SELECT yourColumnName1 from yourTableName WHERE yourColumnName2 IN(value1, value2, .....N) GROUP BY yourColumnName1 HAVING COUNT(DISTINCT yourColumnName2)=conditionValue;To understand the above syntax, let us first create a table. The query to create a table is as follows −mysql> create table DifferentRows -> ( -> FirstRow int, -> SecondRow int -> ); Query OK, 0 rows affected (0.72 sec)Insert some records in the table using insert command. The query is as follows −mysql> insert into DifferentRows values(10, 10); Query OK, 1 row affected ...
Read MoreSELECT increment counter in MySQL?
To select increment counter in MySQL, first you need to declare and initialize a variable. The syntax is as follows −set @anyVariableName=0; select yourColumnName, @anyVariableName:=@anyVariableName+1 as anyVariableName from yourTableName;To understand the above syntax and set an increment counter, let us first create a table. The query to create a table is as follows.mysql> create table incrementCounterDemo -> ( -> Name varchar(100) -> ); Query OK, 0 rows affected (1.01 sec)Insert some records in the table using insert command. The query is as follows.mysql> insert into incrementCounterDemo values('John'); Query OK, 1 row affected (0.18 sec) mysql> insert into incrementCounterDemo values('Carol'); ...
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