I have a table with this structure:
id | IDs | Name | Type
1 | 10 | A | 1
2 | 11 | B | 1
3 | 12 | C | 2
4 | 13 | D | 3
except id nothing else is a FOREIGN or PRIMARY KEY. I want to select a row based on it's column values that are not PRIMARY KEY. I have tried the following syntax but it yields no results.
SELECT * FROM MyTable WHERE Name = 'A', Type = 1;
what am I doing wrong? What is exactly returned by a SELECT statement? I'm totally new to Data Base and I'm currently experimenting and trying to learn it. so far my search has not yield any results regarding this case.
Use and to add multiple conditions to your query
SELECT *
FROM MyTable
WHERE Name = 'A'
AND Type = 1;
Related
I have a table with a large amount of data; moving forward, I would like to enforce uniqueness for a given column in this table. However, the table contains a large amount of rows where that column is non-unique. I am not able to delete or alter these rows.
Is it possible to enforce uniqueness over a given date range, or since a specific date, or based on the value of another column (or something else like that) in MariaDB?
You can create a UNIQUE index on multiple columns, where one column is nullable. MariaDB will see each column with NULL values as a different value regarding the UNIQUE index, even if the other column values of the UNIQUE index are the same. Check the MariaDB documentation Getting Started with Indexes - Unique Index:
The fact that a UNIQUE constraint can be NULL is often overlooked. In SQL any NULL is never equal to anything, not even to another NULL. Consequently, a UNIQUE constraint will not prevent one from storing duplicate rows if they contain null values:
CREATE TABLE t1 (a INT NOT NULL, b INT, UNIQUE (a,b));
INSERT INTO t1 values (3,NULL), (3, NULL);
SELECT * FROM t1;
+---+------+
| a | b |
+---+------+
| 1 | 1 |
| 2 | 1 |
| 2 | 2 |
| 3 | NULL |
| 3 | NULL |
+---+------+
You can create such a UNIQUE index on the date column you already have and a new column which indicates if the date value should be unique or not:
CREATE TABLE Foobar(
id INT AUTO_INCREMENT PRIMARY KEY NOT NULL,
createdAt DATE NOT NULL,
dateUniqueMarker BIT NULL DEFAULT 0,
UNIQUE KEY uq_createdAt(createdAt, dateUniqueMarker)
);
INSERT INTO Foobar(createdAt) VALUES ('2021-11-04'),('2021-11-05'),('2021-11-06');
SELECT * FROM Foobar;
+----+------------+------------------------------------+
| id | createdAt | dateUniqueMarker |
+----+------------+------------------------------------+
| 1 | 2021-11-04 | 0x00 |
| 2 | 2021-11-05 | 0x00 |
| 3 | 2021-11-06 | 0x00 |
+----+------------+------------------------------------+
INSERT INTO Foobar(createdAt) VALUES ('2021-11-05');
ERROR 1062 (23000): Duplicate entry '2021-11-05-\x00' for key 'Foobar.uq_createdAt'
UPDATE Foobar SET dateUniqueMarker = NULL WHERE createdAt = '2021-11-05';
INSERT INTO Foobar(createdAt, dateUniqueMarker) VALUES ('2021-11-05', NULL);
SELECT * FROM Foobar;
+----+------------+------------------------------------+
| id | createdAt | dateUniqueMarker |
+----+------------+------------------------------------+
| 1 | 2021-11-04 | 0x00 |
| 2 | 2021-11-05 | NULL |
| 5 | 2021-11-05 | NULL |
| 3 | 2021-11-06 | 0x00 |
+----+------------+------------------------------------+
Without any data example and scenario illustration, it's hard to know. If you can update your question with those information, please do.
"Is it possible to enforce uniqueness over a given date range, or since a specific date, or based on the value of another column (or something else like that) in MariaDB?"
If by "enforce" you mean to create a new column then populate it with unique identifier, then yes it is possible. If what you really mean is to generate a unique value based on other column, that's also possible. Question is, how unique do you want it to be?
Is it like this unique?
column1
column2
column3
unique_val
2021-02-02
ABC
DEF
1
2021-02-02
CBD
FEA
1
2021-02-03
BED
GER
2
2021-02-04
ART
TOY
3
2021-02-04
ZSE
KSL
3
Whereby if it's the same date (on column1), it should have the same unique value regardless of column2 & column3 data.
Or like this?
column1
column2
column3
unique_val
2021-02-02
ABC
DEF
1
2021-02-02
CBD
FEA
2
2021-02-03
BED
GER
3
2021-02-04
ART
TOY
4
2021-02-04
ZSE
KSL
5
Taking all (or certain) columns to consider the unique value.
Both of the scenario above can be achieved in query without the need to alter the table, adding and populate a new column but of course, the latter is also possible.
How can I create a column that has ranked the information of the table based on two or three keys?
For example, in this table the rank variable is based on Department and Name:
Dep | Name | Rank
----+------+------
1 | Jeff | 1
1 | Jeff | 2
1 | Paul | 1
2 | Nick | 1
2 | Nick | 2
I have found this solution but it's in SQL and I don't think it applies to my case as all information is in one table and the responses seem to SELECT and JOIN combine information from different tables.
Thank you in advance
You can count how many rows come before the current row in the current group:
UPDATE MyTable
SET Rank = (SELECT COUNT(*)
FROM MyTable AS T2
WHERE T2.Dep = MyTable.Dep
AND T2.Name = MyTable.Name
AND T2.rowid <= MyTable.rowid);
(The rowid column is used to differentiate between otherwise identical rows. Use the primary key, if you have one.)
I'm trying to get one row from table that have an id column that duplicate in several rows of a SQlite database, but I am getting all rows in table.
This is my table creation and selection query.
CREATE TABLE IMAGES ( MID INTEGER , IMAGE BLOB, ID INTEGER );
SELECT DISTINCT ID, IMAGE FROM IMAGES;
This what I get
mid | image | id
1 | m1 | 1
2 | m2 | 1
3 | m3 | 1
4 | m4 | 2
5 | m5 | 3
6 | m6 | 3
And this what i want
mid | image | id
1 | m1 | 1
4 | m4 | 2
5 | m5 | 3
DISTINCT applies to all the SELECTed columns, i.e., you get each unique combination of id and image in the data.
To control which columns get deduplicated, use GROUP BY.
You also have to specify which image you want for each ID; if you don't use MIN(), you get a random image:
SELECT id, MIN(image)
FROM images
GROUP BY id;
You need to choose the correct columns
SELECT min(mid) FROM images GROUP BY id;
Then you need to use that to select the correct rows.
SELECT DISTINCT ID, IMAGE FROM IMAGES WHERE mid in (SELECT min(mid) FROM images GROUP BY id);
Otherwise the records from the GROUP BY, could be made up from any (or last) of the rows.
I have A table and two rows with id=1 and id=2 and their x parameter is 1. I also have B table and two rows with same id 1 and 2. I am trying to update all of the data(column)on B table which has same id with A table whose x parameter is 1.
A table
id | x |
1 | 1 |
2 | 1 |
B table
id | Y |
1 | yes|
2 | yes|
My query is
UPDATE B SET y='No' WHERE B.id=(SELECT A.id FROM A WHERE A.x=1);
The problem is select returns mutliple data and i can only update the first data.
I tried to use JOIN but sqlite gives syntax error near INNER i couldn't find the problem.
UPDATE B SET B.y='No' INNER JOIN A ON B.id=A.id WHERE A.x=1;
Use this:
UPDATE ... WHERE B.id IN (SELECT A.id ...);
I have this database in sqlite (table1):
+-----+-------+-------+
| _id | name | level |
+-----+-------+-------+
| 1 | Mike | 3 |
| 2 | John | 2 |
| 3 | Bob | 2 |
| 4 | David | 1 |
| 5 | Tom | 2 |
+-----+-------+-------+
I want to create a view with all elements of level 2 and then to add a new column indicating the order of the row in the new table. That is, I would want this result:
+-------+------+
| index | name |
+-------+------+
| 1 | John |
| 2 | Bob |
| 3 | Tom |
+-------+------+
I have tried:
CREATE VIEW words AS SELECT _id as index, name FROM table1;
But then I get:
+-------+------+
| index | name |
+-------+------+
| 2 | John |
| 3 | Bob |
| 5 | Tom |
+-------+------+
I suppose it should be something as:
CREATE VIEW words AS SELECT XXXX as index, name FROM table 1;
What should I use instead of XXXX?
When ordered by _id, the number of rows up to and including this one is the same as the number of rows where the _id value is less than or equal to this row's _id:
CREATE VIEW words AS
SELECT (SELECT COUNT(*)
FROM table1 b
WHERE level = 2
AND b._id <= a._id) AS "index",
name
FROM table1 a
WHERE level = 2;
(The computation itself does not actually require ORDER BY _id because the order of the rows does not matter when we're just counting them.)
Please note that words is not guaranteed to be sorted; add ORDER BY "index" if needed.
And this is, of course, not very efficient.
You have two options. First, you could simply add a new column with the following:
ALTER TABLE {tableName} ADD COLUMN COLNew {type};
Second, and more complicatedly, but would actually put the column where you want it, would be to rename the table:
ALTER TABLE {tableName} RENAME TO TempOldTable;
Then create the new table with the missing column:
CREATE TABLE {tableName} (name TEXT, COLNew {type} DEFAULT {defaultValue}, qty INTEGER, rate REAL);
And populate it with the old data:
INSERT INTO {tableName} (name, qty, rate) SELECT name, qty, rate FROM TempOldTable;
Then delete the old table:
DROP TABLE TempOldTable;
I'd much prefer the second option, as it will allow you to completely rename everything if need be.