SQL & PL/SQL

Hello,

i've performance problems running the following query :

SELECT ALL_TAB_COLUMNS.OWNER , ALL_TAB_COLUMNS.TABLE_NAME , SUBSTR(ALL_TAB_COLUMNS.COLUMN_NAME,1,30), DECODE(ALL_CONSTRAINTS.CONSTRAINT_TYPE,NULL,'N','P','Y','N') as PKEY FROM SYS.ALL_TAB_COLUMNS
LEFT OUTER JOIN SYS.ALL_CONS_COLUMNS ON
ALL_TAB_COLUMNS.OWNER = ALL_CONS_COLUMNS.OWNER AND
ALL_TAB_COLUMNS.TABLE_NAME = ALL_CONS_COLUMNS.TABLE_NAME AND
ALL_TAB_COLUMNS.COLUMN_NAME = ALL_CONS_COLUMNS.COLUMN_NAME
LEFT OUTER JOIN SYS.ALL_CONSTRAINTS ON
ALL_CONSTRAINTS.OWNER = ALL_CONS_COLUMNS.OWNER AND ALL_CONSTRAINTS.TABLE_NAME = ALL_CONS_COLUMNS.TABLE_NAME AND ALL_CONS_COLUMNS.CONSTRAINT_NAME = ALL_CONSTRAINTS.CONSTRAINT_NAME,
SYS.ALL_TABLES
WHERE ( ALL_TAB_COLUMNS.OWNER = ALL_TABLES.OWNER ) and ( ALL_TAB_COLUMNS.TABLE_NAME = ALL_TABLES.TABLE_NAME )
AND ALL_TAB_COLUMNS.OWNER = 'MYOWNER'

Can you help me?

Thanks in advance
Luigi