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//! Query engine for columnar database.
use std::collections::HashMap;
use crate::error::{Error, Result};
use crate::columnar::table::Table;
/// Comparison operators for predicates.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Operator {
/// Equal to
Eq,
/// Not equal to
Ne,
/// Less than
Lt,
/// Less than or equal to
Le,
/// Greater than
Gt,
/// Greater than or equal to
Ge,
/// Is null
IsNull,
/// Is not null
IsNotNull,
/// Like (string pattern matching)
Like,
/// Not like (string pattern matching)
NotLike,
/// In (value in set)
In,
/// Not in (value not in set)
NotIn,
}
/// A predicate for filtering rows.
#[derive(Debug, Clone)]
pub enum Predicate {
/// Compare a column to a literal value
Compare {
column: String,
op: Operator,
value: Option<Vec<u8>>,
},
/// Logical AND of predicates
And(Vec<Predicate>),
/// Logical OR of predicates
Or(Vec<Predicate>),
/// Logical NOT of a predicate
Not(Box<Predicate>),
/// Always true
True,
/// Always false
False,
}
impl Predicate {
/// Evaluate the predicate for a row.
pub fn evaluate(&self, table: &Table, row_index: u64) -> bool {
match self {
Predicate::Compare { column, op, value } => {
if let Some(col) = table.column(column) {
match op {
Operator::IsNull => col.is_null(row_index),
Operator::IsNotNull => !col.is_null(row_index),
_ => {
if col.is_null(row_index) {
return false;
}
if let Some(row_value) = col.get_bytes(row_index) {
if let Some(compare_value) = value {
match op {
Operator::Eq => row_value == compare_value.as_slice(),
Operator::Ne => row_value != compare_value.as_slice(),
Operator::Lt => row_value < compare_value.as_slice(),
Operator::Le => row_value <= compare_value.as_slice(),
Operator::Gt => row_value > compare_value.as_slice(),
Operator::Ge => row_value >= compare_value.as_slice(),
Operator::Like => {
// Simple implementation of LIKE
if let Ok(row_str) = std::str::from_utf8(row_value) {
if let Ok(pattern) = std::str::from_utf8(compare_value) {
// Very simple pattern matching (not a real LIKE implementation)
row_str.contains(pattern)
} else {
false
}
} else {
false
}
},
Operator::NotLike => {
// Simple implementation of NOT LIKE
if let Ok(row_str) = std::str::from_utf8(row_value) {
if let Ok(pattern) = std::str::from_utf8(compare_value) {
// Very simple pattern matching (not a real LIKE implementation)
!row_str.contains(pattern)
} else {
true
}
} else {
true
}
},
Operator::In => {
// Not implemented in this simple example
false
},
Operator::NotIn => {
// Not implemented in this simple example
true
},
_ => false,
}
} else {
false
}
} else {
false
}
}
}
} else {
false
}
},
Predicate::And(predicates) => {
for predicate in predicates {
if !predicate.evaluate(table, row_index) {
return false;
}
}
true
},
Predicate::Or(predicates) => {
for predicate in predicates {
if predicate.evaluate(table, row_index) {
return true;
}
}
false
},
Predicate::Not(predicate) => !predicate.evaluate(table, row_index),
Predicate::True => true,
Predicate::False => false,
}
}
}
/// A query on a table.
pub struct Query {
/// Table to query
table: Table,
/// Columns to select
columns: Vec<String>,
/// Predicate to filter rows
predicate: Predicate,
/// Maximum number of rows to return
limit: Option<u64>,
/// Number of rows to skip
offset: u64,
}
impl Query {
/// Create a new query.
pub fn new(table: Table, columns: Vec<String>, predicate: Predicate) -> Self {
Query {
table,
columns,
predicate,
limit: None,
offset: 0,
}
}
/// Set the maximum number of rows to return.
pub fn with_limit(mut self, limit: u64) -> Self {
self.limit = Some(limit);
self
}
/// Set the number of rows to skip.
pub fn with_offset(mut self, offset: u64) -> Self {
self.offset = offset;
self
}
/// Execute the query and return the results.
pub fn execute(&self) -> Result<Vec<HashMap<String, Option<Vec<u8>>>>> {
let mut results = Vec::new();
let mut count = 0;
// Get the columns we need
let mut columns = HashMap::new();
for name in &self.columns {
if let Some(column) = self.table.column(name) {
columns.insert(name.clone(), column);
} else {
return Err(Error::InvalidArgument(format!(
"Column {} not found in table {}",
name,
self.table.name()
)));
}
}
// Iterate through rows
for row_index in 0..self.table.row_count() {
// Apply predicate
if self.predicate.evaluate(&self.table, row_index) {
// Apply offset
if row_index < self.offset {
continue;
}
// Create result row
let mut row = HashMap::new();
for (name, column) in &columns {
let value = if column.is_null(row_index) {
None
} else {
column.get_bytes(row_index).map(|bytes| bytes.to_vec())
};
row.insert(name.clone(), value);
}
results.push(row);
count += 1;
// Apply limit
if let Some(limit) = self.limit {
if count >= limit {
break;
}
}
}
}
Ok(results)
}
}
/// Builder for creating a query.
pub struct QueryBuilder {
/// Table to query
table: Table,
/// Columns to select
columns: Vec<String>,
/// Predicate to filter rows
predicate: Predicate,
/// Maximum number of rows to return
limit: Option<u64>,
/// Number of rows to skip
offset: u64,
}
impl QueryBuilder {
/// Create a new query builder.
pub fn new(table: Table) -> Self {
// Default to selecting all columns
let columns = table.schema().fields.iter()
.map(|field| field.name.clone())
.collect();
QueryBuilder {
table,
columns,
predicate: Predicate::True,
limit: None,
offset: 0,
}
}
/// Select specific columns.
pub fn select(mut self, columns: Vec<String>) -> Self {
self.columns = columns;
self
}
/// Add a predicate to filter rows.
pub fn filter(mut self, predicate: Predicate) -> Self {
self.predicate = predicate;
self
}
/// Set the maximum number of rows to return.
pub fn limit(mut self, limit: u64) -> Self {
self.limit = Some(limit);
self
}
/// Set the number of rows to skip.
pub fn offset(mut self, offset: u64) -> Self {
self.offset = offset;
self
}
/// Build the query.
pub fn build(self) -> Query {
Query {
table: self.table,
columns: self.columns,
predicate: self.predicate,
limit: self.limit,
offset: self.offset,
}
}
}