I have 5 tables, each with 10+ columns. They all share some similar columns but each table has columns unique to themselves. The tables are not related to each other, meaning that one record in one table won't be able to exist in another table. Therefore, when I try to concatenate them using UNION ALL, I get a very complicated MySQL statement since the tables have so many columns. For example, I have 2 tables:
Table1: ID, Name, Parts, Comments, End_Date
Table2: ID, Name, Machines, End_Date
If I were to combine these two tables, I would use the MySQL statement
SELECT
ID,
Name,
Parts,
'' as Machines,
Comments,
End_Date
FROM Table1
UNION ALL
SELECT
ID,
Name,
'' as Parts,
Machines,
'' as Comments,
End_Date
FROM Table2
As you can see, the statement gets much larger the more columns and more tables there are. Is there an elegant way to concatenate these tables in a more concise statement? Thanks!
For combining tables, you can use the FOREIGN KEY method from SQL that will work in MySQL. To do this, outside of the creation of your table:
ALTER TABLE Table1
ADD FOREIGN KEY (End_Date) REFERENCES Table2(End_Date);
To do this inside the creation of your table, you would just code it in after your primary key and use the bit that includes FOREIGN KEY and everything after except the ' ; '. This method will only work with one column from each table though.
For extra help that you could research if you so choose to, this website has the basic methods of all SQL languages and is extremely helpful:
SQL Tutorials
Related
In MS-Access, I've got a table where its key input is either a primary key of one type (of companies) or the primary key of another type (of companies). There's virtually no overlap in fields between these two types (hence they're separate tables).
How does one structure this as links etc just relate to one table?
Thank you
Use a union query. The official guide is here:
Use a union query to combine multiple queries into a single result
I have a MySql table called Person, and one day I accidentally deleted someone from this table. I have a backup table, called PersonBak so I was going to restore my deletion from the backup. However, in the course of moving forward on my application I renamed all the fields in Person, except for the primary key, PersonID. Now Person and PersonBak have the same data, but only one matching column name.
Is there any way to restore my missing person to Person from PersonBak without doing a lot of work? I have quite a few columns. Of course I could just do the work now, but I can imagine this coming up again.
Is there some way to tell MySql that these are really the same table, with the columns in the same order, just different column names? Or any way at all to do this without writing out specifics of which columns in PersonBak match which ones in Person?
If the column datatypes are the same between the tables, the column count is the same, and they are all in the same order, then MySQL will do all of the work for you:
INSERT INTO t1 SELECT * FROM t2;
The column names are ignored. The server uses ordinal position only, to decide how to line up the from/to columns.
What about this:
insert into Person(id, col11, col12) (select id, col21, col22 from personBak where id=5)
person schema:
columns (id, col11, col12)
personBak schema:
columns (id, col21, col22)
Look at Mysql SELECT INTO and you can specify the field names & create an insert statement
I have two tables:
Table1 - Sales
id, Timestamp, Notes, CSR, Date, ExistingCustomer, PubCode, Price, Pub, Expiry, Size, KeyCode, UpSell, CustName, CustAddress, CustCity, CustState, CustPostal, CustCountry, CustPhone, CustEmail, CustCardName, CustCardNumber, CustCardType, CustCardExpiry, CustCardCode
Table2 - Refunds
id,Timestamp,CSR,Date,OrderId,Refunded,Saved,Publication
Basically, I want to create a table (MySQL) which will have some columns that are the same between the two tables and which will update automatically with the values from these two columns.
ie. Table3
Timestamp, CSR, Date, Publication
And this table would automatically update whenever a new record is posted into either of the other two tables, so it would essentially be a merged table.
Because there's nothing to join these two tables, I don't think the JOIN function would work here. Is there anyway I can do this?
You can use an trigger which actives on insert on both tables to make it automatically update.
As for combining tables with no common tables, view this question.
You need to use a stored procedure and a trigger on insert/update of the non merged table
There's got to be some way to join it, and in fact you mention Timestamp, CSR, Date, Publication.
You could join on them in a view. You could add table three and then add triggers though that would be an awful mess.
Why do you want to denormalise in this way?
How about Table3 is a unique key to use as a surrogate, and your 4 join fields, and then you take those out of Table 1 and 2 and replace them with the key the suurrogate key in table 3.
Then it'sa simple join query and no data duplication.
Disclaimer: I didn't design these tables, and am aware they're not the best way to store this data. I need advice on the best way to handle the situation.
I have two MySQL tables:
`students`
id int; primary, unique
prof1_id varchar
prof2_id varchar
prof3_id varchar
`professors`
id int; primary, unique, auto-increment
username varchar
fname varchar
fname varchar
students_id int
comment text
A professor's username may be in any of the last three columns in the students table. Professors will need to provide one comment for each student who has them in their row in the students table.
The application that is the front end to this database expects two more columns in the professors table: student_id and comment. Since each student may have any 3 professors in their row, new rows will need to be added to professors whenever they are listed for multiple students. This means that the professors id field will need to auto increment for each new student comment.
What is the best way to accomplish this data transfer with a MySQL query? I've tried looking at UPDATE in combination with JOIN, but I'm not sure there is even a valid way to do this. Also, do I need to create another primary key for professors since the multiple rows will have the same id?
I suspect that a VIEW might be the best way to accomplish this, but the application on the front end expects the information to be stored in the professors table.
One other thing I was considering was that I could create a new table by joining the two tables and have a two-column primary key, students.id, professor.id.
Thanks!
Also, do I need to create another primary key for professors since the
multiple rows will have the same id?
Yes. This is good idea.
I wrote simple query that merges data from first table into 2 columns. This is not complete answer, but it can help you a lot:
SELECT id, prof1id as profid
UNION
SELECT id, prof2id
UNION
SELECT id, prof3id
UNION;
You may use this for view, inserts, but im not familiar with specyfic MySQL syntax and i dont want to misslead you. Please give feedback if it work.
"UNION" removes duplicate rows, you may need to use "UNION ALL" to keep duplicates (like duplicated values in 2 or 3 professors columns).
I have a column in my table called student_id, and I am storing the student IDs associated with a particular record in that column, delimited with a | character. Here are a couple sample entries of the data in that column:
243|244|245
245|1013|289|1012
549|1097|1098|245|1099
I need to write a SQL query that will return records that have a student_id of `245. Any help will be greatly appreciated.
Don't store multiple values in the student_id field, as having exactly one value for each row and column intersection is a requirement of First Normal Form. This is a Good Thing for many reasons, but an obvious one is that it resolves having to deal with cases like having a student_id of "1245".
Instead, it would be much better to have a separate table for storing the student IDs associated with the records in this table. For example (you'd want to add proper constraints to this table definition as well),
CREATE TABLE mytable_student_id (
mytable_id INTEGER,
student_id INTEGER
);
And then you could query using a join:
SELECT * FROM mytable JOIN mytable_student_id
ON (mytable.id=mytable_student_id.mytable_id) WHERE mytable_student_id.student_id = 245
Note that since you didn't post any schema details regarding your original table other than that it contains a student_id field, I'm calling it mytable for the purpose of this example (and assuming it has a primary key field called id -- having a primary key is another requirement of 1NF).
#Donut is totally right about First Normal Form: if you have a one-to-many relation you should use a separate table, other solutions lead to ad-hoccery and unmaintainable code.
But if you're faced with data that are in fact stored like that, one common way of doing it is this:
WHERE CONCAT('|',student_id,'|') LIKE '%|245|%'
Again, I agree with Donut, but this is the proper query to use if you can't do anything about the data for now.
WHERE student_id like '%|245|%' or student_id like '%|245' or student_id like '245|%'
This takes care of 245 being at the start, middle or end of the string. But if you aren't stuck with this design, please, please do what Donut recommends.