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SQL components

SQL components. In Oracle. SQL in Oracle. SQL is made up of 4 components: DDL Data Definition Language CREATE, ALTER, DROP, TRUNCATE. Creates / Alters / Drops tables, views, sequences, indexes and synonyms. DML Data Manipulation Language SELECT, INSERT, UPDATE, DELETE. DCL

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SQL components

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  1. SQL components In Oracle

  2. SQL in Oracle • SQL is made up of 4 components: • DDL • Data Definition Language • CREATE, ALTER, DROP, TRUNCATE. • Creates / Alters / Drops tables, views, sequences, indexes and synonyms. • DML • Data Manipulation Language • SELECT, INSERT, UPDATE, DELETE. • DCL • Data Control Language • GRANT, REVOKE, • Transaction control statements • SET TRANSACTION, COMMIT, ROLLBACK

  3. CREATE TABLE statement • Creates tables in your schema. • The basic Create statement: CREATE TABLE [schema_name].table_name ( {column_name data_type} ) • [] optional, {} one or more, lower case – user supplied names, upper case reserved words, [|] either or, () are part of the syntax. • See www.ss64.com/orasyntax/datatypes.html for a comprehensive list and description of data types.

  4. Adding constraints • To make one the attributes a primary key, put a CONSTRAINT on the table, by adding: • PRIMARY KEY (column_name).

  5. Constraints • Constraints can be imposed when the table is being created, in the CREATE statement. • Constraints can be on the column or the table. • Column constraints can be listed after the column data type; e.g. NOT NULL, UNIQUE, PRIMARY KEY, CHECK…. • Other constraints can be added after all columns have been declared, by ALTERing the table. • These can include • primary keys, including compound primary keys, or • foreign keys.

  6. Exercise • Set up two tables. • Product with columns ProductCode 4 digits, ProductName 15 characters, ProductPrice Decimal – 4 digits with two after the decimal place. The product code is the primary key. • Supplier with columns SupplierId 4 digits, SName 15 characters. SupplierId is the primary key. • Find the tables in the catalog. • To find tables in the catalog, you manipulate the SQLPlus buffer. • Select * from cat

  7. Data Manipulation Language • Data Manipulation language (DML) allows you to manipulate the contents of the tables in you schema, rather than the definition. • DML includes • Insert • Delete • Update • Select

  8. Insert statement • This adds data to the table. • Either a full row can be added, or values can be put in individual columns. • NOTE: If only some of the columns are given values, the remainder of the columns have an undefined status of NULL. • If a column is constrained by the ‘NOT NULL’ constraint, every insert to the owning table must provide a value for that column, unless a DEFAULT value is provided for the table.

  9. Example insert (full version)

  10. Exercise • Insert four rows into the supplier table, ensuring that the data types and constraints are respected. • Insert two rows into the product table, as above. • Check the contents of both tables by • Select * from tablename; • Note that the semicolon ends the statement.

  11. Altering tables • Alter is part of the data definition language. • Alter allows a column to be added or dropped from the table. • ALTER TABLE customer ADD server NUMBER(7) DEFAULT 1234567; • Alter allows a constraint to be added or removed from a table. • ALTER TABLE customer ADD CONSTRAINT servedby FOREIGN KEY server REFERENCES staff(staffId);

  12. Exercise • Use the Alter command to: • Add a new column called ‘supplier’ of type 4 digits, to the product table, with a default value of 1234. • Add a constraint to the product table, making the new ‘supplier’ field a foreign key, referencing the SupplierId in the Supplier table. • Lessons? • If this doesn’t work, why not? • What can you do to make it work?

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