I have often SQL statements of the kind
SELECT LENGTH(col_name) FROM `table` WHERE *condition*
to establish the size of the contents of a specific column in a given row of a mySQL table. However, it is not clear to me that there is a single SQL statement that would fetch the sum of the content lengths of ALL the columns in a given row. I should add that all the columns in question are VARCHARS.
Yes, I know I could do this by fetching the entire row as
SELECT * FROM `table` WHERE *condition*
collapsing the resulting row contents into a string and getting the length of that string but I was wondering if there isn't a more efficient one liner to do the job. Any tips would be much appreciated.
Well, I prefer to use CHAR_LENGTH over LENGTH
SELECT CHAR_LENGTH(CONCAT(col1,col2,col3))
FROM tableName
WHERE...
From the linked question
LENGTH() returns the length of the string measured in bytes.
CHAR_LENGTH() returns the length of the string measured in characters.
Try this solution without going into column names:
SELECT SUM(character_maximum_length) length,
table_name
FROM information_schema.columns
WHERE table_name='your_table_name_here'
AND table_schema=DATABASE()
-- AND column_name IN ('choose', 'columns')
GROUP BY table_name;
Have you tried:
SELECT char_length(col_name)+char_length(col_name2) FROM table WHERE condition
Related
How do I select rows within a column where the string length equals 5 characters?
I am aware of length() and char_length() functions, but they seem to only be for sorting of data query results.
Any help is very appreciated.
SELECT * FROM yourtable WHERE CHAR_LENGTH(yourcolumn)=5
I have a table and in that I want to sort a column in that table. But I’m unable to get the sorted order because there are different kinds of characters in the first place of the string. Some of them have horizontal tab, some of them have spaces, and some of them are empty. I have tried trim method but it doesn’t work for me. I have nearly 200000 records in that table. I cant update the table. I need a select query which should give the result neglecting all the unnecessary things and should sort the columns.
I think this might work
SELECT *
FROM table_name
ORDER BY IF(coloum_name LIKE "_%", substr(coloum_name, 1), coloum_name);
Explanation:
We use the IF function to strip the first character from the beginning of the string before returning the string to the ORDER BY clause. For more complex rules we could create a user-defined function and place that in the ORDER BY clause instead. Then you would have ...ORDER BY MyFunction(coloum_name)
For SQL Server, do this:
SELECT *
FROM table_name
ORDER BY CASE WHEN coloum_name LIKE "_%" THEN substr(coloum_name, 1) ELSE coloum_name END
Is there a way to retrieve the column names of a query that returns no data?
The result of this query would be empty.
Is there a way how to find the column names when there's no result?
Please note that I'm aware of solutions using DESCRIBE and select column_name from information_schema.columns where table_name='person';
but I need a more flexible solution that will fit these multicolumn queries.
Please also note that I am still using the original PHP MySQL extention (so no MySQLi, and no PDO).
If you wrap your query with the following SQL, it will always return the column names from your query, even if it is an empty query result:
select myQuery.*
from (select 1) as ignoreMe
left join (
select * from myTable where false -- insert your query here
) as myQuery on true
Note: When the results of the subquery are empty, a single row of null values will be returned. If there is data in the subquery it won't affect the output because it creates a cross-product with a single row...and value x 1 = value
Execute following command if the result of your previous query is empty
SHOW columns FROM your-table;
For more details check this.
I'm not sure if it will satisfy you but you can do this
SELECT *, COUNT(*) FROM table;
It will return null values (except last column which you can ignore) if the query is empty and you will be able to access all columns. It's not proper way of doing it and selecting names from INFORMATION_SCHEMA would be much better solution.
Please note that result is aggregated and you need to use GROUP BY to get more results if there are any.
You should ,
Select COLUMN_NAME From INFORMATION_SCHEMA.COLUMNS
Where TABLE_SCHEMA='yourdb'
AND TABLE_NAME='yourtablename';
Is there any way to do something like :
SELECT * FROM TABLE WHERE COLUMN_NUMBER = 1;
?
No, you can't. Column order doesn't really matter in MySQL. See the below question for more details.
mysql - selecting values from a table given column number
If your table has a column named COLUMN_NUMBER and you want to retrieve rows from the table where that column contains a value of '1', that query should do the trick.
I suspect that what you are trying to do is reference an expression in the select list with an alias. And that is not supported. An expression in the WHERE clause that references a column must reference the column by name.
We can play some tricks with inline views, to give an alias to an expression, but this is not efficient in terms of WHERE predicates, because of the way MySQL materializes a derived table. And, in that case, its a name given to the column in the inline view that has to be referenced in the outer query.
How I did it:
I'm trying to take (last 3 values of) column number 4 in sometable.
set #mydb=(SELECT DATABASE());
set #mycol=(select COLUMN_NAME from information_schema.columns where
table_schema=#mydb and table_name='sometable' and ordinal_position = 4);
SELECT Date,#mycol FROM sometable ORDER BY Date DESC LIMIT 3;
Of course, if Database name is known, first line could by whiped and #mydb replaced by real database name.
You can do this trick
Example:
$query="select * from employee";
$result=mysql_query($query);
$meta=mysql_fetch_field($result,0) // 0 is first field in table , 1 is second one ,,, etc
$theNameofFirstField=$meta->name; // this well return first field name in table
// now you can use it in other query
$seconQuery="select $theNameofFirstField from employee";
I am trying to query a table in mysql based on the length of a string in a specific column. I know mysql has a function called LENGTH(), but that returns the length of the string. I want to be able to pull data based on the result of the LENGTH() function.
Example:
SELECT * table WHERE LENGTH(word) = 6
of course that does not work. I read through http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function%5Flength but could not find anything to help me.
yes I could make something in PhP to accomplish this, but I would like to do it at the query level.
Any help?
Try:
SELECT *
FROM table
WHERE LENGTH(RTRIM(word)) = 6
I believe you wanted to use query SELECT * FROM tableName WHERE LENGTH(word) = 6; (assuming that the word is name of column in tableName).
This is very unfortunate solution on large tables, you should create new column and use UPDATE tableName SET wordLength = LENGTH( word).