data bases

• What does SELECT do?

  Selects specifid data from specified table
• What does FROM do?


  It specifies the table the information is wanted from
• what does WHERE do?

  specifies the condition the data has to apply to
• what does LIKE do?

  • its an operator
  • is used to search for a specified pattern in a column
• what does AND do?

  • its an operator
  • used to combine two or more conditions in a WHERE clause
  • both conditions must be true
• what does OR do?

  • its an operator
  • used to combine multiple condition but only one has to be true
• what does DELETE do?

  • Used before a WHERE
  • To remove data where the condition is true
• what does INSERT do?

  • it uses its own statement
  • it adds more rows to a table
• what does DROP do?

  • is its own statement
  • it drops a full table or entity
• what does JOIN or INNER JOIN do?

  • Is its own statement
  • It combines rows from two or more tables based on related column
• what does WILDCARDS do?

  • is used with the LIKE operator
  • is used to search for specific patterns
  • it uses % to show for where the pattern could be eg to search if there is an ”a” it would be :WHERE name LIKE ’%a’;
• what is 1st normal form

  A table is in first normal form when there is no repeating attributes or grouped attributes
• what is 2nd normal form

  a table is in 2nd normal form when there is no partial key dependencies
• what is 3rd normal form

  a table is in 3rd normal form when there is no non-key dependencies
• What does it mean for a table to have no partial key dependencies mean?

  It means that the primary key is doing its job so all data in that column is unique
• what does it mean if a table has a non-key dependency

  it means that there is 1 or more column that doesn’t rely on the primary key
• what is an ERD

  entity relationship diagram