Set explain what does it mean?

I have two tables the first, test_tbl1, has an index on column of varchar datatype. The second table, test_tbl2 has index on column of char datatype. Running SET EXPLAIN ON produced the following. -What is the different between the two queries? -What the effect of having index on column of varchar datatype? Thanks in advance, Haytham test_tbl2 is defined with data type char QUERY: ------ select count(*) from test_tbl2 where client_id = '001' and market_id = '001' and lname = 'ADAMS' Estimated Cost: 1 Estimated # of Rows Returned: 1 1) test_tbl2: INDEX PATH (1) Index Keys: client_id market_id lname (Key-Only) Lower Index Filter: (test_prospect.client_id = '001' AND (test_prospect.market_id = '001' AND test_prospect.lname = 'ADAMS' ) ) test_tbl2 is defined with data type varchar QUERY: ------ select count(*) from test_tbl1 where client_id = '001' and market_id = '001' and lname = 'ADAMS' Estimated Cost: 1 Estimated # of Rows Returned: 1 1) test_prospect: INDEX PATH (1) Index Keys: client_id market_id lname Lower Index Filter: (test_prospect.client_id = '001' AND (test_prospect.market_id = '001' AND test_prospect.lname = 'ADAMS' ) )