LEAST(), GREATEST(), BETWEEN() do not work for string values

[ohaibbq]

The current implementation of these function converts the arguments into either Float64() or Int64() types.

The zetasql analyzer will assert that the argument types are homogenous, so we can update our implementations to use .GT(), etc

SELECT GREATEST("a", 2)

No matching signature for function GREATEST for argument types: STRING, INT64. Supported signature: GREATEST([ANY, ...]) [at 1:8]

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SELECT LEAST("a", "b"), GREATEST("a", "b"), "b" between "a" and "c";

Expected

col1	col2	col3
a	b	true

Actual

failed to scan rows: strconv.ParseFloat: parsing "a": invalid syntax

failed to scan rows: strconv.ParseInt: parsing "b": invalid syntax