Adding an Index to AP database - mysql

I am a CS student and I cannot figure out why my statement for adding an index will not work. To be specific, I am supposed to write a script that adds an index to the AP database for the zip code field in the Vendors table. I have attempted to do so using this statement:
CREATE INDEX (index_name) ON (table_name) ((column_name))
Am I missing something and I’m just not seeing it?

Try:
CREATE INDEX index_name ON table_name (column_name)
For example, to create index "i" on table "t" with column "c", you would do:
create index i on t (c)

Related

How to create index for existing table in mysql?

Our server gets slow, "To get data from mysql database". So I search for it on google. They told me, "Use INDEX for the select query to get data from the database it becomes more fastest execution".
Index is a small copy of a database table sorted by key values.
U need to create index first.
CREATE INDEX index_name ON table_name(column_name)
Then:
SELECT * FROM table_name
USE INDEX (index_name)
WHERE condition;

Create functions indexes MySQL

I have a table with [date] index.
[date] column:
'2015-01-05'
'2015-01-06'
and etc
Can I create new index for function index?
When i am trying to create it I get error, example:
create index date_y on table (year(date))
If I could we didn't recreate queries for program performance.
Yes and no. No, you cannot create an index on an expression in this fashion. However, if you happen to have mysql v5.7.8 or newer, then you can create generated columns and you can create a secondary index on them (secondary index means that a generated column cannot be part of a primary key).
So, create your expression as a generated column and then create an index on it - if you have mysql v5.7.8 or newer.
One moment, when I have:
date is created index on tableX
id is created index on tableX
id is created index on tableY
My query:
Select * from tableX as x left outer join tableY as y on x.id=y.id
where year(x.date)=2015 and month(x.date)=11
Should I recreate date to:
create index date on tableX (date,id)
or some else?

How to/ Where to delete/edit an index from MySql which prevents duplicates row

I'm using SugarCRM and a few weeks ago I executed a a query on MySQL which created an index to prevent duplicate rows. Where can I see that or find it and edit or delete this ? I'm not able to remember the exact query but it's needed to add more columns. Using MySQL only just a few weeks.
MySQL error 1062: Duplicate entry 'example-dyplicate' for key
'idx_name'
To see the structure of a table, including all the indexes, use:
SHOW CREATE TABLE tablename;
You can delete an index with:
DROP INDEX indexname ON tablename;
There's no way to edit an index. If you want to change an index, you drop it and then add a new index with the new columns you want. However, you can do both in a single query using ALTER TABLE:
ALTER TABLE tablename DROP INDEX indexname ADD INDEX indexname (col1, col2, ...);

Problems creating an index

The question is:
Write the SQL statement to create an index on the city table for the attribute CountryCode. Name the index CountryCode_idx.
So my statement is:
CREATE INDEX city_name_countrycode_idx ON city (name, countrycode);
but the problem is, when I try to drop the index in the next question using statement
DROP INDEX city_name_countrycode_idx;
I get a syntax error expecting ON
and then I try making a statement called:
DROP INDEX city_name_countrycode_idx ON city;
but my statement affected 0 rows apparently. Can someone tell me if my create index statement is correct and why my drop index statement isn't working?
DROP INDEX city_name_countrycode_idx;
I get a syntax error expecting ON ...
As per documentation on DROP INDEX Syntax:
Name: 'DROP INDEX'
Description:
Syntax:
DROP INDEX index_name ON tbl_name
[algorithm_option | lock_option] ...
algorithm_option:
ALGORITHM [=] {DEFAULT|INPLACE|COPY}
lock_option:
LOCK [=] {DEFAULT|NONE|SHARED|EXCLUSIVE}
DROP INDEX drops the index named index_name from the table tbl_name.
Conclusion:
Hence to drop an index, you must use table name on which the index was created.
And for your index city_name_countrycode_idx to be dropped you have to use the table name city on which the said index is created.
DROP INDEX city_name_countrycode_idx ON city;
0 rows affected means no change in data . Although the index is dropped.
you can cross check by desc the table before and after dropping the index
Thanks

CREATE INDEX with condition?

I am using MySQL v5.1.
I would like to create index on a table by executing the following SQL statement:
CREATE INDEX index_name
ON table_name (column_name)
But, I wan to firstly check if the index on that column has already been created or not, if not, create it (otherwise do not create). What is the SQL syntax for this?
Mysql doesn't have IF NOT EXISTS for CREATE INDEX. You can work it out by querying information_schema.statistics table. Take a look here, there is an example of stored procedure that does what you are looking for (search for "CREATE INDEX IF NOT EXISTS" on the page)
You want SHOW INDEX.
To get all the indexes on a table:
SHOW INDEX FROM table_name
MySQL allows you to add a WHERE clause to limit the results as well.
Lock the table while you're checking to see if the index exists (and if it doesn't exist, creating the index) so that another process doesn't create the index right after you've checked for it but before you've created it yourself.