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    • You can create partitioned indexes on non-partitioned tables. These either be range or hash partitioned. The syntax to do so is:create index <index_name> on <table_name> (<col1>, <col2>, ...)   global partition by (range|hash) (<col1>, <col2>, ...) (partitions N) ( <partitions> );The partitions N clause only applies for hash partitioned indexes. The partitions clause is optional for hash partitioning, but mandatory for range partitioned indexes. 
       
      Topic : Partitioned Indexes
    • Index-organized tables have a PCTTHRESHOLD property. This states the largest percentage of an index block a row can consume. If a row is larger than this, Oracle splits the row in two. The columns that exceed this limit go in an overflow segment. You can also state which column to split a row at with the INCLUDING clause. All columns after this go in the overflow segment. If you specify both PCTTHRESHOLD and INCLUDING, PCTTHRESHOLD takes priority. For example, your index org clause is: pctthreshold 5 including c2 overflowand there is another column, c1, listed before c2 in the table. If c1 causes a row to be greater than 5% of the block, Oracle splits here instead of at c2. Placing columns in an overflow segment frees up space in the index block. Thus Oracle can place more rows in each one.The default value for PCTTHRESHOLD is 50. 
       
      Topic : Index Organized Tables
    • You can create check constraints to ensure strings only store certain characters. There are many ways you can do this. These include:Using regular expressions. These can validate that the string only contains valid characters or it doesn't contain invalid characters. In either case you must take care when writing the regex. These are easy to get wrong!Mapping the valid characters to null. Then checking that the final string is null. 
       
      Topic : Check Constraints
    • We can replace triggers with new DEFAULT options in 12c. This improves performance and centralizes all logic in the table definition instead of in PL/SQL inside triggers.
       
      Topic : Identity Columns
    • Foreign keys allow values that are all null, even when there is no matching null value in the parent table.If you have a compound FK, if any of its values are null in the child, the non-null values don't have to match values in the parent. In this case you can have values in the child not in the parent!
       
      Topic : Referential Integrity
    • You can stop people running select * queries by creating virtual columns with expressions that raise an error.
       
      Topic : Virtual Columns
    • To remove a primary key, you need to run an alter table ... drop command. This can either use:The primary key clause alter table <table_name> drop primary key;The constraint clause. To use this, you must pass the name of the primary key constraint: alter table <table_name> drop constraint <primary_key_name>;
       
      Topic : Primary Keys
    • You can't use the following data types in a primary key column:LOB, LONG, LONG RAW, VARRAY, NESTED TABLE, BFILE, REF, TIMESTAMP WITH TIME ZONE, or user-defined typeYou can use a TIMESTAMP WITH LOCAL TIME ZONE in a primary key.
       
      Topic : Primary Keys
    • A foreign key validates that the values in a set of columns in one table exist in another. To do this, all the columns you reference in the target table must be part of either a:Primary keyUnique constraint
       
      Topic : Referential Integrity
    • Starting in Oracle Database 12c, you can use column defaults to auto-generate surrogate key values. You do this either by:Specifying a sequence as the column default. Creating identity columnsIdentity columns default to "generated always". This prevents you supplying your own values for the surrogate key. If you want to be able to overwrite these, you must specify: generated by default (on null)On null is optional. 
       
      Topic : Identity Columns
    • Functions on columns stop Oracle Database using normal indexes on that column. To overcome this, either the index must:use the same function as the query orhave exactly the same columns as the query
       
      Topic : Function-based Indexes
    • Key to solving deductive logic puzzles is coming up with a strategy for identifying and discarding possibilities in a systematic fashion.
       
      Topic : Deductive Logic
    • Key to solving deductive logic puzzles is coming up with a strategy for identifying and discarding possibilities in a systematic fashion.
       
      Topic : Deductive Logic
    • Key to solving deductive logic puzzles is coming up with a strategy for identifying and discarding possibilities in a systematic fashion.
       
      Topic : Deductive Logic
    • Key to solving deductive logic puzzles is coming up with a strategy for identifying and discarding possibilities in a systematic fashion.
       
      Topic : Deductive Logic
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