Decision function
Format: decode (field, value of 1, a result, the value of 2, 2 ... a result, the default result) If the above values do not match, the results of the final result of the default function.
Aggregation function count () sum () max () min () avg ()
group by grouping field 1, field 2 ... packet
Format: select rows where data from a data source packet group by the filter condition set filter condition field having a field sort order by ..;
--rowid and rownum, fairly and pseudo-column
rowid object corresponding to the address, the address of each table corresponds to a record, when the data inserted into the table when there is rowid, the address conversion is the only each record;
No. rownum result set, as long as there is a result set, the result would have its own set rownum, the result set number of data, starting from 1 rownum, each +1;
Multi Table Links:
92 Syntax: en: there where, to meet the conditions before the show, does not meet does not show
99 Syntax: select the data from Table 1, Table 2, Table 3 ...; join
Outer join
Left outer join | connecting left and right outer joins | the right connection: the main table is called a left join on the left of the comma, the main table is called the right connections in the right comma (+) plus sign is opposite the main table
Main Table: Data in the main table join condition to be satisfied regardless of whether the display