CREATE TABLE base.client
(
  n serial NOT NULL,
  sirname varchar( 255 ) NOT NULL,
  name varchar( 255 ) NOT NULL,
  fd timestamp NOT NULL,
  status int4 NOT NULL,
  card_num varchar( 255 ) NOT NULL,
  rank int4 NOT NULL,
  CONSTRAINT pkey_client_n PRIMARY KEY (n)
) 
WITHOUT OIDS;

CREATE INDEX idx_client_sirname
  ON base.client
  USING btree
  (sirname);

select * from base.client
where  sirname like 'Иванов%'

Seq Scan on client  (cost= 0 . 00 .. 3852 . 61  rows= 520  width= 50 )
  Filter: ((sirname)::text ~~ 'Иванов%'::text)

select * from base.client
where  sirname = 'Иванов'

Index Scan using idx_client_sirname on client  (cost= 0 . 00 .. 1838 . 91  rows= 520  width= 50 )
  Index Cond: ((sirname)::text = 'Иванов'::text)