create triggers.

Hello there.
Can anybody help me with Postgresql triggers?
what I need is a trigger which update value of field
"tables_rows.total_rows" to rows count of table
"zzz" if I insert new row in table "zzz"...

CAREATE TABLE zzz (
    ...
    ...
);
CREATE TABLE tables_rows (
    table_name VARCHAR(32),
    total_rows BIGINT,
    CONSTRAINT pk_total_rows PRIMARY KEY(table_name,
total_rows)
);

Thanks a lots
regars
    Ling.

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