Could not validate table exists in MySQL.
Tried below query but no output.
if !(select * from information_schema.tables where table_name='sy_code')
To see the schema of a table, use query
DESCRIBE table_name;
To see all the existing table in our database, use query
SELECT table_name FROM information_schema.tables WHERE table_schema = 'your_db'
Related
This query gives all the column names from all the databases.
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'Customers'
But I need to get all the column names from a table from a specific database. Because I have multiple tables with the same name. How to do that? Is there anything like
SELECT *
FROM INFORMATION_SCHEMA.COLUMNS
WHERE DATABASE_NAME = 'database_name' TABLE_NAME = 'table_name'
I am using xampp server and phpMyAdmin.
Quote the fine manual:
26.3.8 The INFORMATION_SCHEMA COLUMNS Table
...
The COLUMNS table has these columns:
TABLE_CATALOG
The name of the catalog to which the table containing the column belongs. This value is always def.
TABLE_SCHEMA
The name of the schema (database) to which the table containing the column belongs.
...
..you should see it when you do SELECT * ?
You want something like this.
SELECT TABLE_NAME, COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
AND TABLE_NAME = 'whatever'
ORDER BY TABLE_SCHEMA, TABLE_NAME, ORDINAL_POSITION;
The MySQL INFORMATION_SCHEMA uses columns named TABLE_SCHEMA to hold the database for each table.
This is the SQL for my expected result
SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA='database_name' AND TABLE_NAME = 'table_name';
I have multiple tables in my multiple databases.
On different servers, i use MySQL / PostgreSQL / MS SQL.
I keep short table namesbut the comments given to the tables are with full explanation.
I want query that will show me tables ending with "com" and also the comment given to each table (table's comment).
In MySQL, I know:
SELECT table_name FROM information_schema.tables where table_name like "%com"
But this shows all tables from all databases.
For MySQL, check out following:
SELECT table_name FROM information_schema.tables;
will show all table names in all databases;
SELECT table_name,table_comment FROM information_schema.tables
will show all table names + comment in all databases;
interesting thing, you can fire
SELECT * FROM information_schema.tables;
to know what all info you can get of a table.
SELECT table_name,table_comment FROM information_schema.tables
where
table_schema = 'sifr_b';
will show all table names + comment in "sifr_b" database;
SELECT table_name,table_comment FROM information_schema.tables
where
table_schema = 'sifr_b' and
table_name like "%com";
will show those table names + comment in "sifr_b" database, that have table name ending with "com";
I want to drop all databases with zero tables I was able to get the databases with tables using
SELECT table_schema, count(table_name) FROM information_schema.tables group by table_schema
But how can I delete the dbs not in this list. I can't do it manually because there are more then 500 dbs there.
About to know schemas without tables, you can try this:
SELECT * FROM information_schema.schemata S
WHERE NOT EXISTS
(SELECT 'TABLE' from information_schema.tables T
WHERE T.table_schema = S.schema_name)
Because in system table SCHEMATA you'll find all schemas of your server and in table TABLES you'll find all tables in all schemas
The upper query must be input on cursor, so you must use a prepared statement to execute your cursor, because your DROP DATABASE has a variable (your schema_table) and it can be ran only with a prepared statement
Used the method posted by #dnoeth in the comments with a slightly diffrent query to get the drop commands and then with some Notepad++ magic executed them to drop all empty databases
SELECT concat('drop database ',schema_name) FROM information_schema.schemata
WHERE schema_name NOT IN
(SELECT TABLE_SCHEMA FROM information_schema.tables)
I know how to use queries but I've never had to use one for this particular tasks .. I know about the SHOW TABLES; command .. How can I write a query to check if a particular table exists in a MYSQL database .. For example , a query that checks if table MEMBERS exists in database called USERS ??
You can use INFORMATION_SCHEMA.TABLES
USE USERS;
SELECT * FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_NAME = 'MEMBERS'
Searching Table:
select * from
information_schema.tables
where table_name like '%MEMBERS%'
Searching Column:
select * from
information_schema.columns
where table_name like '%COLUMN%'
This query generates an error because table2 doesn't exist:
Select * FROM table WHERE table2.id IS NOT NULL
Is there anything like this for check the table2 before apply the check on the id?
Select * FROM table WHERE (EXIST(table2) AND table2.id IS NOT NULL) or not EXIST(table2)
You need to query this system table:
SELECT table_name
FROM information_schema.tables
WHERE table_schema = 'yourdatabasename'
AND table_name = 'table2';
If a row is returned, then your table exists.
I do not believe there is any command or function in standard SQL to do this. You could query the data dictionary to check if the table exists before issuing your SQL query as follows:
SELECT table_name FROM INFORMATION_SCHEMA.tables WHERE table_name = 'xxx';
I do not think it could be done in a single SQL statement though.