Table information retrieval in mySQL - mysql

Question

ALL,
I just tried following query:
SELECT cols.column_name, cols.data_type, cols.character_maximum_length, cols.character_octet_length,
cols.numeric_precision, cols.numeric_scale, cols.column_default, cols.is_nullable,
cols.ordinal_position, kcu.column_name
FROM information_schema.columns cols, information_schema.key_column_usage kcu
WHERE kcu.constraint_name = 'PRIMARY' AND kcu.table_schema = cols.table_schema AND
kcu.table_name = cols.table_name AND cols.table_schema = 'draft' AND cols.table_name = 'leagues';
The last column of that query does return the primary key column name.
However, what I'd like to see instead is this:
If the column is a primary key then the query will output '1' in the last query column.
If the column is not a primary key, then the query will output '0' in the last query column.
Is there a function inside mySQL that will help me do that?
Thank you.

Answer 1

Never use commas in the FROM clause. Always use proper, explicit JOIN syntax.
The "function" is case:
SELECT cols.column_name, cols.data_type, cols.character_maximum_length, cols.character_octet_length,
cols.numeric_precision, cols.numeric_scale, cols.column_default, cols.is_nullable,
cols.ordinal_position,
(CASE WHEN kcu.column_name IS NULL THEN 0 ELSE 1 END) as pk_flag
FROM information_schema.columns cols LEFT JOIN
information_schema.key_column_usage kcu
ON kcu.constraint_name = 'PRIMARY' AND kcu.table_schema = cols.table_schema AND
kcu.table_name = cols.table_name
WHERE cols.table_schema = 'draft' AND cols.table_name = 'leagues';

Answer 2

This is the query I will use:
SELECT cols.column_name, cols.data_type, cols.character_maximum_length, cols.character_octet_length,
cols.numeric_precision, cols.numeric_scale, cols.column_default, cols.is_nullable,
cols.ordinal_position,
(CASE WHEN kcu.column_name = cols.column_name THEN 1 ELSE 0 END) as pk_flag
FROM information_schema.columns cols, information_schema.key_column_usage kcu
WHERE kcu.constraint_name = 'PRIMARY' AND kcu.table_schema = cols.table_schema AND
kcu.table_name = cols.table_name AND cols.table_schema = 'draft' AND cols.table_name = 'leagues';
It works as expected in mySQL Workbench.

Answer 3

Note: This is not an answer to your question.
#Igor, here are my tests regarding running a select query using FROM on two tables (table1, resp. table2), compared with a select command called by LEFT JOIN-ing the same tables.
As you mentioned, there is indeed a difference: LEFT JOIN-ing implies the existence of one or more relations between the tables, but FROM-ing do not (in the context).
My question is, why would/should data from uncorrelated tables be fetched?
Table creation:
-- Create table1 table.
CREATE TABLE `tests`.`table1` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NULL,
PRIMARY KEY (`id`));
-- Create table2 table.
CREATE TABLE `tests`.`table2` (
`id` INT(11) NOT NULL AUTO_INCREMENT,
`name` VARCHAR(50) NULL,
PRIMARY KEY (`id`));
Value insertions:
-- Insert values into table1 table.
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('1', 'TAB1 1');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('2', 'TAB1 2');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('3', 'TAB1 3');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('4', 'TAB1 4');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('5', 'TAB1 5');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('6', 'TAB1 6');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('7', 'TAB1 7');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('8', 'TAB1 8');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('9', 'TAB1 9');
INSERT INTO `tests`.`table1` (`id`, `name`) VALUES ('10', 'TAB1 10');
-- Insert values into table2 table.
INSERT INTO `tests`.`table2` (`id`, `name`) VALUES ('1', 'TAB2 1');
INSERT INTO `tests`.`table2` (`id`, `name`) VALUES ('2', 'TAB2 2');
INSERT INTO `tests`.`table2` (`id`, `name`) VALUES ('3', 'TAB2 3');
Table previews:
FROM query & result:
JOIN query & result: