Hi everybody,
I am Hugo . I want to know something more about SQL.
please can anybody give me some idea about some basic SQl questions?
First of all i want to know,
1.What is the SQL Data Manipulation Language(DML)?
2.What is the SQL Data Defenition Language(DDL)?
hugvc333
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Jump to PostDML or Data manipulation language is nothing but "How do you manipulate the data in a table". You can manipulate the data in these ways.
1. Selecting the data from the table (Select)
2. Inserting the data to the table (Insert)
3. Updating the data in the table (Update)
4. …
Jump to PostNormalization is a difficult theory to explain. You should read it yourself to understand it better. But in short, normalization is a process following which, you can optimize the performance of your database. (Eg. By avoiding obsolete data, duplication, and by using primary keys, etc).
Index is just like …
Jump to PostOh, btw, if you have any duplicate rows, *I dont think it is possible to delete only the duplicate rows. You have to manually (:() delete them. *
Edit: The only way i can think of is, create a dummy table(new_table). Copy distinct rows from old_table to new_table. Truncate …
Jump to PostTo avoid duplication in column(s) we can create it with unique costraint. Constraint is nothing but rules that you can impose on the columns to be unique or not null etc. To create a unique column you can have the codes like:
create table mytable(col1 datatype unique, col2 datatype,...)Or …
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