query none null values in mysql - mysql

I tried to implement the following mysql command try to get rows with none null values,
here is the table tbtext:
id text
1
2 number2
3 number3
4
create table tbtext(
id unsigned int auto_increment primary key,
text char(7)
)
I tried select * from tbtext where text is not null, but it returns the whole rows and doesn't return row 3 and row 4. I am new to mysql, can anyone help me with it, thanks in advance.


I'm assuming text contains empty strings, and not NULL. The best thing to do would be to replace those empty strings with NULL, but you could also use this query :
-- ...
WHERE text <> '';
Please note however that empty strings are information, where NULL means lack of information. You should definitely not have empty strings if that's not what you're trying to do.

Related

Issue with integer column return with alphanumeric value

I have a query where there are 2 conditions used one for id and another for project_id , id is type int(10) and project_id is type varchar(250) and I having issue with this query please see the image. According to normal login it should only return the row with id 57 but its returning 2 rows which wrong. Can anyone please help me out

Try it
select * from `projects` where `id` = 57 and `project_id` = '7QJYouUh'
You have input wrong id And you want to log in so, you to set condition 'and'.

Using SQL to select records with a single "true" bit field from several bit fields

If I have a table like this:
CREATE TABLE `Suppression` (
`SuppressionId` int(11) NOT NULL AUTO_INCREMENT,
`Address` varchar(255) DEFAULT NULL,
`BooleanOne` bit(1) NOT NULL DEFAULT '0',
`BooleanTwo` bit(1) NOT NULL DEFAULT '0',
`BooleanThree` bit(1) NOT NULL DEFAULT '0',
PRIMARY KEY (`SuppressionId`),
)
Is there a set-based way in which I can select all records which have exactly one of the three bit fields = 1 without writing out the field names?
For example given:
1 10 Pretend Street 1 1 1
2 11 Pretend Street 0 0 0
3 12 Pretend Street 1 1 0
4 13 Pretend Street 0 1 0
5 14 Pretend Street 1 0 1
6 14 Pretend Street 1 0 0
I want to return records 4 and 6.

You could "add them up":
where cast(booleanone as unsigned) + cast(booleantwo as unsigned) + cast(booleanthree as unsigned) = 1
Or, use tuples:
where ( (booleanone, booleantwo, booleanthree) ) in ( (0b1, 0b0, 0b0), (0b0, 0b1, 0b0), (0b0, 0b0, 0b1) )
I'm not sure what you mean by "set-based".

If your number of booleans can vary over time and you don't want to update your code, I suggest you make them lines and not columns.
For example:
CREATE TABLE `Suppression` (
`SuppressionId` int(11) NOT NULL AUTO_INCREMENT,
`Address` varchar(255) DEFAULT NULL,
`BooleanId` int(11) NOT NULL,
`BooleanValue` bit(1) NOT NULL DEFAULT '0',
PRIMARY KEY (`SuppressionId`,`BooleanId`),
)
So with 1 query and a 'group by' you can check all values of your booleans, however numerous they are. Of course, this makes your tables bigger.
EDIT: Just came out with another idea: why don't you have a checksum column added, whose value would be the sum of all your bits? So you would update it at every write into your table, and just check this one in your select

If you
must use this denormalized way of representing these flags, and you
must be able to add new flag columns to your table in production, and you
cannot rewrite your queries by hand when you add columns,
then you must figure out how to write a program to write your queries.
You can use this query to retrieve a result set of boolean-valued columns, then you can use that result set in a program to write a query involving all those columns.
SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = DATABASE()
AND TABLE_NAME = 'Suppression'
AND COLUMN_NAME LIKE 'Boolean%'
AND DATA_TYPE = 'bit'
AND NUMERIC_PRECISION=1
The approach you have proposed here will work exponentially more poorly as you add columns, unfortunately. Any time a software engineer says "exponential" it's time to run away screaming. Seriously.
A much more scalable approach is to build a one-to-many relationship between your Suppression rows and your flags. Add this table.
CREATE TABLE SuppressionFlags (
SuppressionId int(11) NOT NULL,
FlagName varchar(31) NOT NULL,
Value bit(1) NOT NULL DEFAULT '0',
PRIMARY KEY (SuppressionID, FlagName)
)
Then, when you want to insert a row with some flag variables, do this sequence of queries.
INSERT INTO Suppression (Address) VALUES ('some address');
SET #SuppressionId := LAST_INSERT_ID();
INSERT INTO SuppressionFlags (SuppressionId, FlagName, Value)
VALUES (#SuppressionId, 'BooleanOne', 1);
INSERT INTO SuppressionFlags (SuppressionId, FlagName, Value)
VALUES (#SuppressionId, 'BooleanTwo', 0);
INSERT INTO SuppressionFlags (SuppressionId, FlagName, Value)
VALUES (#SuppressionId, 'BooleanThree', 0);
This gives you one Suppression row with three flags set in the SuppressionFlags table. Note the use of #SuppressionId to set the Id values in the second table.
Then to find all rows with just one flag set, do this.
SELECT Suppression.SuppressionId, Suppression.Address
FROM Suppression
JOIN SuppressionFlags ON Suppression.SuppressionId = SuppressionFlags.SuppressionId
GROUP BY Suppression.SuppressionId, Suppression.Address
HAVING SUM(SuppressionFlags.Value) = 1
It gets a little trickier if you want more elaborate combinations. For example, if you want all rows with BooleanOne and either BooleanTwo or BooleanThree set, you need to do something like this.
SELECT S.SuppressionId, S.Address
FROM Suppression S
JOIN SuppressionFlags A ON S.SuppressionId=A.SuppressionId AND A.FlagName='BooleanOne'
JOIN SuppressionFlags B ON S.SuppressionId=B.SuppressionId AND B.FlagName='BooleanTwo'
JOIN SuppressionFlags C ON S.SuppressionId=C.SuppressionId AND C.FlagName='BooleanThree'
WHERE A.Value = 1 AND (B.Value = 1 OR C.Value = 1)
This common database pattern is called the attribute / value pattern. Because SQL doesn't easily let you use variables for column names (it doesn't really have reflection) this kind of way of naming your attributes is your best path to extensibility.
It's a little more SQL. But you can add as many new flags as you need, in production, without rewriting queries or getting a combinatorial explosion of flag-matching. And SQL is built to handle this kind of query.

how to make default text column where comparision binary (case sensitive and trim)

Sorry if this is duplicated, but I don't know how to find about the question.
Hi, this my table:
CREATE TABLE `log_Valor` (
`idLog_Valor` int(11) NOT NULL AUTO_INCREMENT,
`Valor` text binary NOT NULL,
PRIMARY KEY (`idLog_Valor`)
)
ENGINE=InnoDB;
INSERT INTO `log_Valor` (Valor) VALUES ('teste');
INSERT INTO `log_Valor` (Valor) VALUES ('teste ');
I have 2 rows:
1 | 'teste'
2 | 'teste '
When I run:
SELECT * FROM log_Valor where valor = 'teste'
It returns the two rows.
How do I make default comparison case sensitive and to not trim without having to specify in the query BINARY?

Use LIKE instead of =.
SELECT * FROM log_Valor WHERE valor LIKE 'teste';
From the documentation
In particular, trailing spaces are significant, which is not true for CHAR or VARCHAR comparisons performed with the = operator
DEMO

Convert char(5) to tinyint(4) in mysql

I'm trying to insert rows from one table to the other. In the first table, the datatype of one column is char(5), but the same column has tinyint(4) datatype in the second table. When i run the insert query, it says
Incorrect integer value: '' for column 'x' at row 258
I cannot alter or modify the datatype now as it violates some constraints. Is there a way to use cast or convert char to tinyint?
Thanks.

You probably want something like this:
INSERT INTO newtable
SELECT CASE WHEN x = '' THEN 0 ELSE x END
FROM oldtable
I'm assuming that you want blanks to turn into zeros? If not, then provide the integer value you want blanks to have.
If there are other exceptions, use more alternatives in the CASE expression.

MySQL: SUM in WHERE clause

I've got this table
CREATE TABLE `subevents` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`title` varchar(150) DEFAULT NULL,
`content` text,
`class` tinyint(4) NOT NULL DEFAULT '1',
PRIMARY KEY (`id`)
) ENGINE=MyISAM
Each row can have a different value in the 'class' field.
I'd like to select any number of rows, ordered randomly, as long as the sum of the values in the 'class' field is equal to 100.
How could I accomplish it directly in the MySQL query without doing it later in PHP?
Thanks everybody!

By "ordered randomly" I assume you mean that the order of the rows doesn't matter but no row can be used more than once. So you are looking for a combination of rows in which the sum of class equals 100. Use the brute force method. Randomly generate possible solutions until you find one that works.
delimiter //
CREATE PROCEDURE subsetsum(total)
BEGIN
DECLARE sum INTEGER;
REPEAT
CREATE OR REPLACE VIEW `solution`
AS SELECT * FROM `subevents`
WHERE 0.5 <= RAND();
SELECT SUM(`class`) INTO sum FROM `solution`;
UNTIL sum = total END REPEAT;
END
//
delimiter ;
CALL subsetsum(100); /* For example */
SELECT * FROM `solution`;
I have tested this with tables having a TINYINT column of random values and it is actually reasonably fast. The only problem is that there is no guarantee that subsetsum() will ever return.

I don't think this is possible with only SQL...the only thing which comes to my mind is to redo a the sql query as long the sum isn't 100
But I have no clue how to select a random number of rows at once.