We generally set the primary key of a database table as “auto-increment”. The auto-increment column of your MySQL table has a maximum value based on the integer type. When you have a lot of data in your table, the auto-increment value can be exhausted by reaching its maximum value. After that, no data can be … Read more
I got the error “Trigger already exists” error while I was re-importing a MySQL database. A solution to this problem is to create DROP queries for all the Triggers of the database. SELECT Concat('DROP TRIGGER ', Trigger_Name, ';') FROM information_schema.TRIGGERS WHERE TRIGGER_SCHEMA = 'your_database_name'; This will print out the DROP statements for all the triggers. … Read more
MongoDB is an open-source document database. Document in MongoDB means a row or record in the database. A document contains data in key-value pairs. MongoDB is popular for it’s high performance, scalability and availability. This article shows how to perform simple select, insert, update, delete database operations in MongoDB. That’s also referred as CRUD (Create, … Read more
This article shows SQL query to get size (in MB) of all MySQL databases. It also shows the query to get the size (in MB) of all the tables present in any particular database. Get size (in MB) of all MySQL databases SELECT table_schema "Database Name", sum( data_length + index_length ) / 1024 / 1024 … Read more
This article shows:- – How to add column to mysql database table after the table has already been created – How to delete column from mysql database table after the table has already been created – How to add foreign key to table column after the table has already been created Basically, all this can … Read more
Some definitions of foreign key:- A FOREIGN KEY in one table points to a PRIMARY KEY in another table. A foreign key is a field in a relational table that matches the primary key of another table. The foreign key can be used to cross-reference tables. A table may have multiple foreign keys, and each … Read more
The JOIN keyword is used in an SQL statement to query data from two or more tables, based on a relationship between certain columns in these tables. [@via w3schools] A SQL JOIN clause combines records from two or more tables in a database. It creates a set that can be saved as a table or … Read more
This article shows how to backup/export and restore/import single & multiple databases and tables in MySQL. Backup/Export 1) Backup/Export single database mysqldump -h hostname -u username -p database_name > /path/backup.sql 2) Backup/Export multiple databases mysqldump -h hostname -u username -p –databases db1 db2 db3 > /path/threedb.sql Here: db1, db2, db3 are three different database name. … Read more