Displays all the databases on MongoDB
Answer:
To display all the active databases on a MongoDB server, type
show dbs
To use it, like MySQL, try
use test
(Assume you need to use the test db)
Apr 012011
Mar 302011
Create an index on a document in MongoDB
Answer:
To create an index on a document in MongoDB, you can enter the shell and execute the statement like:
db.test.ensureIndex({ "fieldName": 1 })
(Assume you need to create index on fieldName of the test collection.)
That's easy?
Mar 062011
List all the database size in MySQL
Answer:
The following command will list out all the databases size in MySQL
mysql> SELECT table_schema "Data Base Name", sum( data_length + index_length) / 1024 / 1024
"Data Base Size in MB" FROM information_schema.TABLES GROUP BY table_schema Output:
+--------------------+----------------------+
| Data Base Name | Data Base Size in MB |
+--------------------+----------------------+
| test | 152.59375000 |
| information_schema | 0.00781250 |
| mysql | 0.61196423 |
+--------------------+----------------------+
Mar 042011
Force MySQL to use a specific index during query processing
Answer:
Sometimes, the index picked by MySQL might not be the most optimized one, and you want to pick the index to use by yourself.
To do so, you can provide the index hints by doing something like the following.
mysql> SELECT * FROM user FORCE INDEX user_name WHERE name = 'John' AND user_name = 'john2';
So you tell MySQL to use the index user_name, instead of name (if also available).
That's all.
Mar 022011
Disable Query Cache at runtime when querying MySQL database
Answer:
When you want MySQL to execute a SQL statement without looking at the query cache first, you can use the keyword SQL_NO_CACHE
E.g.
mysql> SELECT SQL_NO_CACHE name FROM user;
That's all.
