SQL - Get databases which contain a specific record - mysql

Question

So originally I have this as a test run.
SELECT DISTINCT table_schema FROM information_schema.columns WHERE table_schema LIKE '%or';
I have looked around and found queries to show all the databases that contain a specific table.
However is it possible to have a query to go a step further and do the following:
"Select all those databases that have a particular table in them and that, in that table, have a particular record in a particular column."?

Answer 1

You cannot do what you want with a SQL statement.
But, you can use SQL to generate the statement that you want. The basic statement is:
select "tablename"
from tablename
where columnname = value
limit 1
Note that value may need to have single quotes around it. You can generate this with:
select concat('select "', c.table_name, '" ',
'from ', c.schema_name, '.', c.table_name, ' ',
'where ', c.column_name, ' = ', VALUE, ' '
'limit 1'
)
from information_schema.columns c
where c.table_name = TABLENAME and c.column_name = COLUMN_NAME;
To put all the statements in one long SQL statement, use:
select group_concat(concat('select "', c.table_name, '" as table_name',
'from ', c.schema_name, '.', c.table_name, ' ',
'where ', c.column_name, ' = ', VALUE, ' '
'limit 1'
) SEPARATOR ' union all '
)
from information_schema.columns c
where c.table_name = TABLENAME and c.column_name = COLUMN_NAME;
I would then just copy the resulting SQL statement and run it. If you like, you can add a prepare statement and run it dynamically.

Answer 2

as an example,
I have a table named T1 with columns (C1,C2), and I am searching for the value 'Needle'.
What this store procedure does is search through table names that starts with T and columns that starts with C, then loop through them and finds the value 'Needle'. It then returns the table_Schema,table_name,column_name and how many times the value 'Needle' is found within that column_name,table_name,table_schema combination.
see this sqlFiddle
CREATE PROCEDURE findDatabase(IN in_value varchar(50))
BEGIN
DECLARE bDone INT;
DECLARE _TableSchema VARCHAR(50);
DECLARE _TableName VARCHAR(50);
DECLARE _ColumnName VARCHAR(50);
DECLARE curs CURSOR FOR SELECT TABLE_SCHEMA,TABLE_NAME,COLUMN_NAME FROM information_schema.columns WHERE TABLE_NAME LIKE "T%" AND COLUMN_NAME LIKE "C%";
DECLARE CONTINUE HANDLER FOR NOT FOUND SET bDone = 1;
DROP TEMPORARY TABLE IF EXISTS tblResults;
CREATE TEMPORARY TABLE IF NOT EXISTS tblResults (
id int auto_increment primary key,
tableSchema varchar(50),
tablename varchar(50),
columnname varchar(50),
timesFound int
);
OPEN curs;
SET bDone = 0;
REPEAT
FETCH curs INTO _TableSchema,_TableName,_ColumnName;
SET #found = 0;
SET #sql = CONCAT("SET #found = (SELECT COUNT(*) FROM ",_TableSchema,".",_TableName,
" WHERE ",_ColumnName,"='",in_value,"')");
PREPARE statement FROM #sql;
EXECUTE statement;
IF (#found > 0) THEN
INSERT INTO tblResults(tableSchema,tableName,columnName,TimesFound) VALUES (_TableSchema,_TableName,_ColumnName,#found);
END IF;
UNTIL bDone END REPEAT;
CLOSE curs;
SELECT DISTINCT TableSchema,TableName,ColumnName,TimesFound FROM tblResults;
DROP TABLE tblResults;
END//