Oracle PL/SQL Tutorial/System Tables Data Dictionary/all tab columns

Get information on all the columns in tables you have access to using all_tab_columns.

SQL>
SQL> desc all_tab_columns;
 Name                        Null?    Type
 ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------- --------------------------------------------------------------------------------------------------------------------
 OWNER                       NOT NULL VARCHAR2(30)
 TABLE_NAME                  NOT NULL VARCHAR2(30)
 COLUMN_NAME                 NOT NULL VARCHAR2(30)
 DATA_TYPE                            VARCHAR2(106)
 DATA_TYPE_MOD                        VARCHAR2(3)
 DATA_TYPE_OWNER                      VARCHAR2(30)
 DATA_LENGTH                          NOT NULL NUMBER
 DATA_PRECISION                       NUMBER
 DATA_SCALE                           NUMBER
 NULLABLE                             VARCHAR2(1)
 COLUMN_ID                            NUMBER
 DEFAULT_LENGTH                       NUMBER
 DATA_DEFAULT                         LONG
 NUM_DISTINCT                         NUMBER
 LOW_VALUE                            RAW(32)
 HIGH_VALUE                           RAW(32)
 DENSITY                              NUMBER
 NUM_NULLS                            NUMBER
 NUM_BUCKETS                          NUMBER
 LAST_ANALYZED                        DATE
 SAMPLE_SIZE                          NUMBER
 CHARACTER_SET_NAME                   VARCHAR2(44)
 CHAR_COL_DECL_LENGTH                 NUMBER
 GLOBAL_STATS                         VARCHAR2(3)
 USER_STATS                           VARCHAR2(3)
 AVG_COL_LEN                          NUMBER
 CHAR_LENGTH                          NUMBER
 CHAR_USED                            VARCHAR2(1)
 V80_FMT_IMAGE                        VARCHAR2(3)
 DATA_UPGRADED                        VARCHAR2(3)
 HISTOGRAM                            VARCHAR2(15)
SQL>
SQL> --select * from all_tab_columns;