Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
Database Articles
Page 203 of 547
How to define and query json columns in PostgreSQL?
The ability to define JSON columns in PostgreSQL makes it very powerful and helps PostgreSQL users experience the best of both worlds: SQL and NoSQL.Creating JSON columns is quite straightforward. You just have to create/ define it like any other column and use the data type as JSON.Let us create a new table in PostgreSQL, called json_test −CREATE TABLE json_test( serial_no SERIAL PRIMARY KEY, name VARCHAR, metadata JSON );Now, let us populate it with some data −INSERT INTO json_test(name, metadata) VALUES ('Yash', '{"marks_scored":{"science":50, "maths":65}}'), ('Isha', '{"marks_scored":{"science":70, "maths":45}}');As you can see, the JSON values are added within single ...
Read MoreHow to change the type of a column in PostgreSQL?
In order to change the type of a column, the syntax isALTER TABLE table_name ALTER COLUMN column_name TYPE new_data_type USING expression;Please note that altering the type of a column is not recommended generally, especially if your table has a lot of entries already.The USING part of the syntax is optional. It is used when you need to use an expression for converting the existing entries in that column from the current type to the new type. For instance, if you convert a column of type INTEGER to type BIGINTEGER, you need not use any expression for the conversion of existing ...
Read MoreHow to add column to an existing table in PostgreSQL?
The syntax to add a new column to an existing table is quite straightforward.ALTER TABLE table_name ADD COLUMN column_name column_type column_constraint;Say you have existing table marks. An example is given below −serial_nonameroll_nomarks_obtainedperc_marksmax_marksdate_of_entry1Yash2642421002021-01-302Isha5617587.52002021-01-30Now, suppose you want to add a column named subject. You can do that using −ALTER TABLE marks ADD COLUMN subject VARCHAR;Now if you query the table again using, SELECT * from marksYou will see the following output −serial_nonameroll_nomarks_obtainedperc_ marksmax_ marksdate_ of_ entrysubject1Yash2642421002021-01-30[null]2Isha5617587.52002021-01-30[null]Note that the values in the subject column are null because we have just created the column, not populated it. We can populate it using the UPDATE ...
Read MoreHow to Kill queries in pgAdmin in PostgreSQL?
Sometimes, some rogue queries can take too long to execute. If the queries are blocking in nature, i.e., they restrict access to a table while they are executing, then any other query on the same table will be put on hold, and this leads to a pile-up of queries. This can, depending on your DB load, even cause the max connections to be exceeded. Luckily, you can easily kill long queries in pgAdmin.Go to Dashboard in your pgAdmin. At the bottom, in the Server Activity section, under the Sessions Tab, you can see all the Active queries.Now, notice the cross ...
Read MoreHow to Query a DB in pgAdmin in PostgreSQL?
Querying a DB in pgAdmin is quite straightforward. Locate your DB in the Servers dropdown on the left, and extend its dropdown, till you see the Schemas dropdown.Once you click on Schemas, the black button on the top, with the DB symbol and the play arrow will become clickable.Click on that button, and you will see a Query Tab open up. That’s it, you can type your queries for this particular DB in that box, and click the play arrow button to execute the queries.The output will be seen on the bottom, in the ‘Data Output’ section.
Read MoreSet user-defined variable with table name in MySQL prepare statement?
Let us first create a table −mysql> create table DemoTable ( StudentId int NOT NULL AUTO_INCREMENT PRIMARY KEY, StudentName varchar(20) ); Query OK, 0 rows affected (0.71 sec)Insert some records in the table using insert command −mysql> insert into DemoTable(StudentName) values('Chris'); Query OK, 1 row affected (0.21 sec) mysql> insert into DemoTable(StudentName) values('David'); Query OK, 1 row affected (0.06 sec) mysql> insert into DemoTable(StudentName) values('Sam'); Query OK, 1 row affected (0.13 sec) mysql> insert into DemoTable(StudentName) values('Mike'); Query OK, 1 row affected (0.12 sec)Display all records from the table using select statement −mysql> select * from DemoTable;This will ...
Read MoreCondition to check for due date and current date records in MySQL where clause
To check for such conditions, use IF() in MySQL.Let us create a table −Examplemysql> create table demo89 -> ( -> duedate date -> ); Query OK, 0 rows affected (0.78Insert some records into the table with the help of insert command −Examplemysql> insert into demo89 values('2020-01-10'); Query OK, 1 row affected (0.55 mysql> insert into demo89 values(null); Query OK, 1 row affected (0.13 mysql> insert into demo89 values('2020-11-29'); Query OK, 1 row affected (0.15 mysql> insert into demo89 values('2019-11-29'); Query OK, 1 row affected (0.09Display records from the table using select statement −Examplemysql> select ...
Read MoreCreating a table with MySQL - Hibernate
To create a table, you need to insert below line into application.properties −spring.jpa.hibernate.ddl-auto=updateHere, Hibernate will create the table demo88 automatically. The application.properties code is as follows −spring.datasource.platform=mysql spring.jpa.database-platform=org.hibernate.dialect.MySQL5InnoDBDialect spring.jpa.hibernate.ddl-auto=update server.port=8191 spring.datasource.driverClassName=com.mysql.jdbc.Driver spring.datasource.url=jdbc:mysql://localhost:3306/sampledatabase spring.datasource.username=root spring.datasource.password=123456The demo88 entity class is as follows to create table columns −Examplepackage com.automaticallytablecreation; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.Id; import javax.persistence.Table; @Entity @Table public class demo88 { @Id private int id; @Column(name="name") private String name; }The main class code is as follows −Examplepackage com.automaticallytablecreation; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; @SpringBootApplication public class AutomaticTableApplication { public static void main(String[] ...
Read MoreHow to check if any value is Null in a MySQL table single row?
For this, you can use ISNULL in MySQL.Let us create a table −Examplemysql> create table demo86 -> ( -> value1 varchar(20) -> , -> value2 varchar(20) -> ); Query OK, 0 rows affected (2.77Insert some records into the table with the help of insert command −Examplemysql> insert into demo86 values(null, null); Query OK, 1 row affected (0.34 mysql> insert into demo86 values(null, 'John'); Query OK, 1 row affected (0.16 mysql> insert into demo86 values('David', 'Mike'); Query OK, 1 row affected (0.17 mysql> insert into demo86 values('Sam', null); Query OK, 1 row affected ...
Read MoreMySQL - SUM rows with same ID?
To sum rows with same ID, use the GROUP BY HAVING clause.Let us create a table −Examplemysql> create table demo84 -> ( -> id int, -> price int -> ) -> ; Query OK, 0 rows affected (0.60Insert some records into the table with the help of insert command −Examplemysql> insert into demo84 values(1, 2000); Query OK, 1 row affected (0.08 mysql> insert into demo84 values(1, 2000); Query OK, 1 row affected (0.14 mysql> insert into demo84 values(2, 1800); Query OK, 1 row affected (0.14 mysql> insert into demo84 values(2, 2200); Query ...
Read More