I have a database named DELTASTORE in mysql in my cpanel. There are tables like ADMIN,CATAGORY,PRODUCT,ORDER. I have inserted some values in each table.
If I run sql
SELECT * FROM ADMIN
it works nicely.
But if I run sql
SELECT * FROM ORDER
it doesn't work! Instead of that, if I run sql
SELECT * FROM DELTASTORE.ORDER
then it works correctly.
Why does that occur?
Is it important to write database name before table name and give a dot between them all the time?
To leave out the database prefix, you have to set a default database, with
USE databasename
When writing programs to access the database, the API provides a way to do this. For instance, in PHP PDO you specify the default database in the DSN:
mysql:host=hostname;dbname=defaultDB
In MySQLi it's an argument to mysqli_connect(). In the obsolete mysql extension you use mysql_use_database(). There are similar methods in other programming languages.
Additionally, since ORDER is a MySQL keyword, you either have to put it in backticks:
SELECT * FROM `ORDER`
or prefix it with a database:
SELECT * FROM DELTASTORE.ORDER
It's usually best to avoid using MySQL reserved words as table or column names, to prevent problems like this. See Syntax error due to using a reserved word as a table or column name in MySQL
The reason is, that ORDER is a SQL keyword (for ORDER BY, which you use to sort the result lines). So with the database name (or schematic name) you mean the table ORDER.
It's better to not use keywords for the table.
Just need to put brackets.
Select * from `ORDER`
Related
Correct me if I'm wrong, but my understanding is that, in MSSQL, sub-structures of a database like Views, Schemas and Tables can be referenced using object notation such as:
Database.Schema.Table.Column
Each of these objects I believe has their own properties.
I need to replicate the structure of an MSSQL DB in MySQL and I am unsure what is the best practice.
I am thinking about creating tables in MySQL with the following naming convention:
Database
|---SubStructureX.Table
| |---Column_A
| |---Column_B
|---SubStructureY.Table
| |---Column_C
| |---Column_D
|
|
Therefore a MySQL query could look like this:
SELECT Column_A, Column_B FROM SubStructureX.Table
In short, "SubstructureX.Table" is just a table name that contains a dot. I would be doing this for ease of use during replication of the MSSQL structure. I don't care if the things before and after the dot are not objects in MySQL.
Is this good MySQL practice?
In MySQL? No, I would think that it's not good practice to use periods in table names at all. I would think that it's very bad practice. The dot is the reference operator in SQL. That means if you want to refer to a column using fully qualified notation, you do so like this:
SELECT Table.Column_A ...
Or, with backtick quoting:
SELECT `Table`.`Column_A` ...
Now, imagine if your table is named StructureX.Table. Just like with a space, you've got to quote that to escape it because you don't want MySQL to think the dot is an operator. That means your SQL has to look like this:
SELECT `StructureX.Table`.Column_A ...
Or, with backtick quoting:
SELECT `StructureX.Table`.`Column_A` ...
Doesn't that look like a syntax error to you? Like maybe it's supposed to be like this:
SELECT `StructureX`.`Table`.`Column_A` ...
This would be a nightmare to maintain and as a systems analyst I would hate any application or developer that inflicted this nomenclature on me. It makes me want to claw my eyes out.
Microsoft SQL Server is different because it supports multiple schemas within a single database, while MySQL treats schema as a synonym for database. In MS SQL Server, schemas are collections of objects, and you can use them to organize your tables, or apply security to tables as a group. The default schema is dbo, which is why you see that one listed so often. In MS SQL Server syntax, this:
SELECT [StructureX].[Table].[Column_A] ...
Means within the current database, the schema named StructureX, table named Table, and column name Column_A. MS SQL Server actually supports a four part name, with the fourth part being the database:
SELECT [MyDatabase].[StructureX].[Table].[Column_A] ...
Here, MyDatabase is the database name.
That same style works in MySQL, except you have to remember that schema and database are synonymous. So there, this:
SELECT `StructureX`.`Table`.`Column_A` ...
Would mean database StructureX, table Table, and column Column_A.
I Can say yes:
But instead of using table name, make a table some alias like this,
select a.column1 from yourTable as a
Using table alias is a good practice.
I refactored a project and wanted to try out PostgreSQL instead of MySQL. I now want to migrate the table contents of some tables.
The problem is, when I use a select query like this (don't bother about the names, is just an example)
SELECT id AS id_x, name AS name_x, name2 AS name2_x
I want to export the table data and import it into MySQL. The problem is, that the syntax for INSERT INTO is different in MySQL and PostgreSQL. I don't want to export the whole table, because I also changed some parts of the structure, tried to make it more performant etc. So I just want to get the table data, but I need those AS x thing, because the names of the columns have changed
I already found several links on this topic.
I can use mysqldump to dump the table and set the --compatible=name parameter. The problem here is, that I can't add a SELECT statement, right? I can only add a where check.
Then, I could use the mysql command to export the query I want, but mysql doesn't have any compatible parameter. How would I achieve that?
You could consider to create a temporaty table by issuing
SELECT id AS id_x, name AS name_x, name2 AS name2_x FROM oldtable INTO temptable
And then as a second step export the temptable using mysqldump with the --compatible= parameter.
See https://dev.mysql.com/doc/refman/5.7/en/select-into.html
My client requests to change from using MySQL to PostgreSQL. The database migration ran well, and my codes are using DevArt dotConnect Universal. Things are looking good except for the actual SQL statement.
In my C# code I used,
"SELECT * FROM users WHERE user_name LIKE '%abc%';"
and it worked with MySQL, but when it is connected to the PostgreSQL, I have to change the SQL statement to use,
"SELECT * FROM public.\"users\" WHERE user_name LIKE '%abc%';"
and the searched text is case-sensitive!
How do I,
(a) make the searched text case insensitive?
(b) avoid needing to add [public.] in front of the table name and to double-quote the table name?
I have seen someone posted something here, Accessing a table without specifying the schema name
but I have 120 tables and it will be time consuming. Is there any faster approach to solve my 2 issues described above?
EDIT:
Oh I realized these two statements yields the same result.
SELECT * FROM Public.user;
and
SELECT * FROM \"user\";
(a) make the searched text case insensitive?
ILIKE keyword in PostgreSQL provides case insensitive search
SELECT * FROM users WHERE user_name ILIKE '%abc%';
or
select * from words where LOWER(word) LIKE '%aba%'
Note: if your table name is Users then use SELECT * FROM "Users"
> SQLFIDDLE DEMO
I managed to connect to MySQL DB via Sql Developer following this guide. MySQL DB shows and I can expolre tables via the navigator. However, I could not run SELECT statement to show any of these tables. In MySQL workbench I used to use :
use [database_name]
Then, run select statement in that database. But in Sql developer, I am not sure what should I add to the statement to make it work. I have tried the following:
select *
from [table_name].[database_name];
It does not work. I found this tutorial, but nothing is mentioned about simple select statement. Any help is deeply appreciated.
AFAIK, except MySQL specific commands; all other standard SQL commands like SELECT,INSERT,UPDATE,DELETE should work just fine using SQL Developer. but per your posted query, it looks total strange.
Your query
select * from [table_name]#[database_name];
remove that # sign.
you should qualify like database_name.table_name.
Unless it's a typo, remove those [] as well from your query
statement.
Your query should look like
select * from database_name.table_name;
You can always write your SQL including database as well, in the form of:
database.tablename
such as:
select * from wordpressdb.usertable where username="someone"
The table names in my mysql database are dynamically generated. Is there some way to select data from tables which have a name matching a pattern? I guess it will look like:
select * from 'table_id_%'
No, you can't do that with MySQL. Tables in a query can't be dynamically specified - you have to build the list in your application (or do several single-table queries).
You can use INFORMATION_SCHEMA TABLES table to find tables you want, here is documentation: http://dev.mysql.com/doc/refman/5.0/en/tables-table.html . TABLES table has column NAME which represents names of tables. After finding table names you can run any sql queries you like.
That's not possible in the way you'd like to do it. However you could probably use prepared statements which are basically query-templates where you specificy the parameters (AFAIK also table names) that get replaced depending on your needs without copy and pasting the same query over and over again for different tables.