private async Task <string> GetNullableColumnHasValueQueryCore(Identifier tableName, Identifier columnName)
{
var quotedTableName = Dialect.QuoteName(Identifier.CreateQualifiedIdentifier(tableName.Schema, tableName.LocalName));
var quotedColumnName = Dialect.QuoteIdentifier(columnName.LocalName);
var filterSql = $"select * from { quotedTableName } where { quotedColumnName } is not null";
var sql = $"select case when exists ({ filterSql }) then 1 else 0 end as dummy";
var suffix = await _fromQuerySuffixAsync.ConfigureAwait(false);
return(suffix.IsNullOrWhiteSpace()
? sql
: sql + " from " + suffix);
}