How to make such as: IF (table if exists types) THEN ... END ?
Try this:
SELECT COUNT(*)
FROM information_schema.tables
WHERE table_schema = '[database name]'
AND table_name = '[table name]';
Save the result and you can use it in an if statement
Related
In MySQL, I can get the auto-increment value by:
SELECT `AUTO_INCREMENT`
FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'DatabaseName'
AND TABLE_NAME = 'TableName';
How do I query this information in Sequel? When I tried DB.run and DB.get, it didn't seem to work.
If nothing else, Sequel makes it easy to send raw SQL:
DB["SELECT `AUTO_INCREMENT` FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA = 'DatabaseName' AND TABLE_NAME = 'TableName'"]
From the documentation:
Using raw SQL
DB.run "CREATE TABLE users (name VARCHAR(255) NOT NULL, age INT(3) NOT NULL)"
dataset = DB["SELECT age FROM users WHERE name = ?", name]
dataset.map(:age)
DB.fetch("SELECT name FROM users") do |row|
p row[:name]
end
Iam working on MYSQL and need a stored procedure that will traverse through table A which has 100 columns and 50,000+ rows and for all Null values found in the table the SP will update it with blank values.
eg
UPDATE table A SET column1=' ' where column1 IS NULL;
column1 is mixture of null and filled and blank rows,but i want to update only null rows.
I do not want to hardcode the column names..want to fetch the columns one by one in the stored procedure itself.is this possible?
You could dynamically fetch the column names from your tables.
SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'my_database' AND TABLE_NAME = 'my_table';
And combine this using inner queries.
Use the mysql ifnull function.You will need the below for all hundred columns. This can be used on string/char as well as integer fields.
update table
set
field1=ifnull(field1, " "),
field2=ifnull(field2, " "),
field3=ifnull(field3, 0),
field4=ifnull(field4, "")....
If you don't want to hardcode the column names, you can build the above query as per the other answer:
SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'my_database' AND TABLE_NAME = 'my_table';
For each of the above rows, build a concatenated update statement.
DEClARE usercursor CURSOR FOR
SELECT COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_SCHEMA = 'my_database' AND TABLE_NAME = 'my_table';
declare updatesql varchar(3000);
set updatesql = "update TABLE set ";
OPEN usercursor
get_users:LOOP
FETCH usercursor into v_username;
set updatesql = concat(v_username,"=ifnull(",updatesql)
set updatesql = concat(v_username,",' '),",updatesql)
END LOOP get_users
I'm trying to check weather thw column exists or not
IF (SELECT COUNT(*) FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'tb_consumer' AND COLUMN_NAME='businness_id' > 0 ) THEN
PRINT 'test'
Whats wrong with above sql? getting error as
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF (Select COUNT(*) From INFORMATION_SCHEMA.COLUMNS Where TABLE_NAME = 'tb_consu' at line 1
New to SQL. Thanks for any help,
Version of MySql is 5.X
You can fix the query by moving the closing paren:
IF (SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tb_consumer' AND COLUMN_NAME = 'businness_id'
) > 0 THEN
PRINT 'test'
A better way to write the condition is using exists:
IF EXISTS (SELECT 1
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tb_consumer' AND COLUMN_NAME = 'businness_id'
) THEN
If you try to use this as part of a stored procedure, you might take a look at the if statement in the mysql documentation
if you do this as part of a normal query, you can write it like
SELECT IF (COUNT(*) > 0, 'TEST, 'TEST FAILED') FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'tb_consumer' AND COLUMN_NAME='businness_id'
i would suggest using CASE statement in MYSQL
SELECT CASE
WHEN COLUMN_NAME = 'businness_id' then 'TEST'
END
from FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tb_consumer'
Case statements are faster on smaller databases
SQL command is not a Boolean function.
Therefore you need to check the value.
Like this:
IF (SELECT COUNT(*)
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'tb_consumer' AND COLUMN_NAME='businness_id') >= 0
THEN PRINT 'test'
I dont know how can i explain it, may be this example garbage query can help.
SELECT if_exists(Fieldname) * FROM my table name
I am trying to select all the rows of the database only if Fieldname field is present.
Can you help me out
SHOW columns from `yourtable` where field='yourfield'
You will get a empty rows, if you dont have that field in that table.
The following code in plain PHP should work fine:
$chkcol = mysql_query("SELECT * FROM `table_name` LIMIT 1");
$mycol = mysql_fetch_array($chkcol);
if(isset($mycol['column_name']))
$results = mysql_query("SELECT * FROM `table_name`");
else
$results = false;
IF EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = ‘you_table_name’ AND COLUMN_NAME = ‘FIELDNAME’)
BEGIN
select fieldname from your_table_name
END
You can use the SHOW COLUMNS expression.
Also i found this solution: http://snippets.dzone.com/posts/show/4663
You need something like this. Sorry, cannot test if the syntax is OK though.
SELECT * FROM table WHERE EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS WHERE table_name=table AND column_name=column)
Thats a query I used: it returns no column, if the column doesn't exist.
It shouldn't be much work to change it, for you needs.
SET #VAR_SQL := Concat('SELECT first_row',CONCAT(IFNULL((SELECT CONCAT(',',COLUMN_NAME) FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'my_table'
AND COLUMN_NAME = 'my_column'),'')),' FROM my_table;');
PREPARE QUERY_STATEMENT FROM #VAR_SQL;
EXECUTE QUERY_STATEMENT;
How do I check if an index exists on a table field in MySQL?
I've needed to Google this multiple times, so I'm sharing my Q/A.
Use SHOW INDEX like so:
SHOW INDEX FROM [tablename]
Docs: https://dev.mysql.com/doc/refman/5.0/en/show-index.html
Try:
SELECT * FROM information_schema.statistics
WHERE table_schema = [DATABASE NAME]
AND table_name = [TABLE NAME] AND column_name = [COLUMN NAME]
It will tell you if there is an index of any kind on a certain column without the need to know the name given to the index. It will also work in a stored procedure (as opposed to show index)
show index from table_name where Column_name='column_name';
SHOW KEYS FROM tablename WHERE Key_name='unique key name'
will show if a unique key exists in the table.
Use the following statement:
SHOW INDEX FROM *your_table*
And then check the result for the fields: row["Table"], row["Key_name"]
Make sure you write "Key_name" correctly
To look at a table's layout from the CLI, you would use
desc mytable
or
show table mytable
Adding to what GK10 suggested:
Use the following statement: SHOW INDEX FROM your_table
And then check the result for the fields: row["Table"],
row["Key_name"]
Make sure you write "Key_name" correctly
One can take that and work it into PHP (or other language) wrapped around an sql statement to find the index columns. Basically you can pull in the result of SHOW INDEX FROM 'mytable' into PHP and then use the column 'Column_name' to get the index column.
Make your database connection string and do something like this:
$mysqli = mysqli_connect("localhost", "my_user", "my_password", "world");
$sql = "SHOW INDEX FROM 'mydatabase.mytable' WHERE Key_name = 'PRIMARY';" ;
$result = mysqli_query($mysqli, $sql);
while ($row = $result->fetch_assoc()) {
echo $rowVerbatimsSet["Column_name"];
}
Try to use this:
SELECT TRUE
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
WHERE TABLE_SCHEMA = "{DB_NAME}"
AND TABLE_NAME = "{DB_TABLE}"
AND COLUMN_NAME = "{DB_INDEXED_FIELD}";
You can use the following SQL to check whether the given column on table was indexed or not:
select a.table_schema, a.table_name, a.column_name, index_name
from information_schema.columns a
join information_schema.tables b on a.table_schema = b.table_schema and
a.table_name = b.table_name and
b.table_type = 'BASE TABLE'
left join (
select concat(x.name, '/', y.name) full_path_schema, y.name index_name
FROM information_schema.INNODB_SYS_TABLES as x
JOIN information_schema.INNODB_SYS_INDEXES as y on x.TABLE_ID = y.TABLE_ID
WHERE x.name = 'your_schema'
and y.name = 'your_column') d on concat(a.table_schema, '/', a.table_name, '/', a.column_name) = d.full_path_schema
where a.table_schema = 'your_schema'
and a.column_name = 'your_column'
order by a.table_schema, a.table_name;
Since the joins are against INNODB_SYS_*, the match indexes only came from the INNODB tables only.
If you need to check if a index for a column exists as a database function, you can use/adopt this code.
If you want to check if an index exists at all regardless of the position in a multi-column-index, then just delete the part AND SEQ_IN_INDEX = 1.
DELIMITER $$
CREATE FUNCTION `fct_check_if_index_for_column_exists_at_first_place`(
`IN_SCHEMA` VARCHAR(255),
`IN_TABLE` VARCHAR(255),
`IN_COLUMN` VARCHAR(255)
)
RETURNS tinyint(4)
LANGUAGE SQL
DETERMINISTIC
CONTAINS SQL
SQL SECURITY DEFINER
COMMENT 'Check if index exists at first place in sequence for a given column in a given table in a given schema. Returns -1 if schema does not exist. Returns -2 if table does not exist. Returns -3 if column does not exist. If index exists in first place it returns 1, otherwise 0.'
BEGIN
-- Check if index exists at first place in sequence for a given column in a given table in a given schema.
-- Returns -1 if schema does not exist.
-- Returns -2 if table does not exist.
-- Returns -3 if column does not exist.
-- If the index exists in first place it returns 1, otherwise 0.
-- Example call: SELECT fct_check_if_index_for_column_exists_at_first_place('schema_name', 'table_name', 'index_name');
-- check if schema exists
SELECT
COUNT(*) INTO #COUNT_EXISTS
FROM
INFORMATION_SCHEMA.SCHEMATA
WHERE
SCHEMA_NAME = IN_SCHEMA
;
IF #COUNT_EXISTS = 0 THEN
RETURN -1;
END IF;
-- check if table exists
SELECT
COUNT(*) INTO #COUNT_EXISTS
FROM
INFORMATION_SCHEMA.TABLES
WHERE
TABLE_SCHEMA = IN_SCHEMA
AND TABLE_NAME = IN_TABLE
;
IF #COUNT_EXISTS = 0 THEN
RETURN -2;
END IF;
-- check if column exists
SELECT
COUNT(*) INTO #COUNT_EXISTS
FROM
INFORMATION_SCHEMA.COLUMNS
WHERE
TABLE_SCHEMA = IN_SCHEMA
AND TABLE_NAME = IN_TABLE
AND COLUMN_NAME = IN_COLUMN
;
IF #COUNT_EXISTS = 0 THEN
RETURN -3;
END IF;
-- check if index exists at first place in sequence
SELECT
COUNT(*) INTO #COUNT_EXISTS
FROM
information_schema.statistics
WHERE
TABLE_SCHEMA = IN_SCHEMA
AND TABLE_NAME = IN_TABLE AND COLUMN_NAME = IN_COLUMN
AND SEQ_IN_INDEX = 1;
IF #COUNT_EXISTS > 0 THEN
RETURN 1;
ELSE
RETURN 0;
END IF;
END$$
DELIMITER ;
You can't run a specific show index query because it will throw an error if an index does not exist. Therefore, you have to grab all indexes into an array and loop through them if you want to avoid any SQL errors.
Heres how I do it. I grab all of the indexes from the table (in this case, leads) and then, in a foreach loop, check if the column name (in this case, province) exists or not.
$this->name = 'province';
$stm = $this->db->prepare('show index from `leads`');
$stm->execute();
$res = $stm->fetchAll();
$index_exists = false;
foreach ($res as $r) {
if ($r['Column_name'] == $this->name) {
$index_exists = true;
}
}
This way you can really narrow down the index attributes. Do a print_r of $res in order to see what you can work with.